[Bug]: inaccurate round()

[skirpichev]

Describe the bug

This was catched by mpmath test suite (https://github.com/mpmath/mpmath/actions/runs/29551924365/job/87796835668):

Python 3.12.8 (Tue Jun 23 15:26:01 UTC 2026)
[Graal, Oracle GraalVM, Java 25.0.3 (amd64)] on 'linux'
Type "help", "copyright", "credits" or "license" for more information.
>>> round(8.98846567431158e+307)
89884656743115800000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

vs

Python 3.12.13 (tags/v3.12.13:3bb231a6a5d, May 14 2026, 11:06:30) [GCC 14.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> round(8.98846567431158e+307)
89884656743115795386465259539451236680898848947115328636715040578866337902750481566354238661203768010560056939935696678829394884407208311246423715319737062188883946712432742638151109800623047059726541476042502884419075341171231440736956555270413618581675255342293149119973622969239858152417678164812112068608

(mpmath's result correctly matches that)

Operating system

Linux

CPU architecture

x86_64

GraalPy version

25.1.3

JDK version

No response

Context configuration

No response

Steps to reproduce

See issue description

Expected behavior

Do correct math

Stack trace

Additional context

No response