I think it uses the largest remainder method to round up to 100%
So option 1 had 49 or 50 votes
50/87 gives 57.47%
49/87 gives 56.32%
and option 2 had 37 or 38 votes
38/87 gives 43.67%
37/87 gives 42.52%
as 0.52>0.47 50-37 is possible 42.52% would have been rounded up to 43%
as 0.67>0.32 49-38 would have given 56%-44%
In more complicated setup best way to be sure might be to use the data explorer though.