[test] few round half-to-even asserts for sprintf

since this seems to be a failure point for JRuby (jrubyGH-5556)

test/jruby/test_sprintf.rb

@@ -15,5 +15,26 @@ def test_sprintf_two
     s = format("%01.0f", n).to_s
     assert(s === "1234567892", "Test failed, value of #{s} did not match '1234567892'.")
   end
+
+  def test_round_half_even
+    assert_equal("5.00", sprintf("%.2f",5.005))
+    assert_equal("5.01", sprintf("%.2f",5.0059))
+    assert_equal("5.01", sprintf("%.2f",5.0051))
+    assert_equal("5.00", sprintf("%.2f",5.0050))
+    assert_equal("5.01", sprintf("%.2f",5.00501))
+    assert_equal("5.000", sprintf("%.3f",5.0005))
+
+    assert_equal("5.02", sprintf("%.2f",5.015))
+    assert_equal("5.02", sprintf("%.2f",5.025))
+
+    assert_equal("97.66A", "%.2fA" % 97.6562)
+    assert_equal("29.56B", "%.2fB" % 29.5562)
+
+    assert_equal "28.554", sprintf("%.3f", 28.5535)
+    assert_equal "97.7X", sprintf("%.1fX", 97.65625)
+
+    assert_equal("28.554", "%.3f" % 28.5535)
+    assert_equal("97.7X", "%.1fX" % 97.65625)
+  end
 end