diff --git a/oauthlib/oauth2/rfc6749/clients/base.py b/oauthlib/oauth2/rfc6749/clients/base.py
index d5eb0cc1..1d12638e 100644
--- a/oauthlib/oauth2/rfc6749/clients/base.py
+++ b/oauthlib/oauth2/rfc6749/clients/base.py
@@ -589,11 +589,11 @@ def populate_token_attributes(self, response):
 
         if 'expires_in' in response:
             self.expires_in = response.get('expires_in')
-            self._expires_at = time.time() + int(self.expires_in)
+            self._expires_at = round(time.time()) + int(self.expires_in)
 
         if 'expires_at' in response:
             try:
-                self._expires_at = int(response.get('expires_at'))
+                self._expires_at = round(float(response.get('expires_at')))
             except:
                 self._expires_at = None
 
diff --git a/oauthlib/oauth2/rfc6749/parameters.py b/oauthlib/oauth2/rfc6749/parameters.py
index 8f6ce2c7..0f0f423a 100644
--- a/oauthlib/oauth2/rfc6749/parameters.py
+++ b/oauthlib/oauth2/rfc6749/parameters.py
@@ -345,7 +345,7 @@ def parse_implicit_response(uri, state=None, scope=None):
         params['scope'] = scope_to_list(params['scope'])
 
     if 'expires_in' in params:
-        params['expires_at'] = time.time() + int(params['expires_in'])
+        params['expires_at'] = round(time.time()) + int(params['expires_in'])
 
     if state and params.get('state', None) != state:
         raise ValueError("Mismatching or missing state in params.")
@@ -437,6 +437,9 @@ def parse_token_response(body, scope=None):
         else:
             params['expires_at'] = time.time() + int(params['expires_in'])
 
+    if isinstance(params.get('expires_at'), float):
+        params['expires_at'] = round(params['expires_at'])
+
     params = OAuth2Token(params, old_scope=scope)
     validate_token_parameters(params)
     return params
diff --git a/tests/oauth2/rfc6749/clients/test_base.py b/tests/oauth2/rfc6749/clients/test_base.py
index 70a22834..7286b991 100644
--- a/tests/oauth2/rfc6749/clients/test_base.py
+++ b/tests/oauth2/rfc6749/clients/test_base.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 import datetime
+from unittest.mock import patch
 
 from oauthlib import common
 from oauthlib.oauth2 import Client, InsecureTransportError, TokenExpiredError
@@ -353,3 +354,35 @@ def test_create_code_challenge_s256(self):
         code_verifier = client.create_code_verifier(length=128)
         code_challenge_s256 = client.create_code_challenge(code_verifier=code_verifier, code_challenge_method='S256')
         self.assertEqual(code_challenge_s256, client.code_challenge)
+
+    def test_parse_token_response_expires_at_is_int(self):
+        expected_expires_at = 1661185149
+        token_json = ('{   "access_token":"2YotnFZFEjr1zCsicMWpAA",'
+                      '    "token_type":"example",'
+                      '    "expires_at":1661185148.6437678,'
+                      '    "scope":"/profile",'
+                      '    "example_parameter":"example_value"}')
+
+        client = Client(self.client_id)
+
+        response = client.parse_request_body_response(token_json, scope=["/profile"])
+
+        self.assertEqual(response['expires_at'], expected_expires_at)
+        self.assertEqual(client._expires_at, expected_expires_at)
+
+    @patch('time.time')
+    def test_parse_token_response_generated_expires_at_is_int(self, t):
+        t.return_value = 1661185148.6437678
+        expected_expires_at = round(t.return_value) + 3600
+        token_json = ('{   "access_token":"2YotnFZFEjr1zCsicMWpAA",'
+                      '    "token_type":"example",'
+                      '    "expires_in":3600,'
+                      '    "scope":"/profile",'
+                      '    "example_parameter":"example_value"}')
+
+        client = Client(self.client_id)
+
+        response = client.parse_request_body_response(token_json, scope=["/profile"])
+
+        self.assertEqual(response['expires_at'], expected_expires_at)
+        self.assertEqual(client._expires_at, expected_expires_at)
diff --git a/tests/oauth2/rfc6749/clients/test_service_application.py b/tests/oauth2/rfc6749/clients/test_service_application.py
index b97d8554..84361d8b 100644
--- a/tests/oauth2/rfc6749/clients/test_service_application.py
+++ b/tests/oauth2/rfc6749/clients/test_service_application.py
@@ -166,7 +166,7 @@ def test_request_body_no_initial_private_key(self, t):
     @patch('time.time')
     def test_parse_token_response(self, t):
         t.return_value = time()
-        self.token['expires_at'] = self.token['expires_in'] + t.return_value
+        self.token['expires_at'] = self.token['expires_in'] + round(t.return_value)
 
         client = ServiceApplicationClient(self.client_id)