Thanks for the patch, George!

This patch fixes the problem in some, but not all cases.  I'd like to take 
this a little further.

As far as I can see, getting correctly rounded results in all cases is out 
of reach without either writing lots of multi-precision code (which would 
make the round code unnecessarily complicated and difficult to maintain) 
or using Python's arbitrary-precision integers (which would be slow).

But it would be reasonable to aim for correctly rounded results