This assumes you haven't already maxed out the GPA value for the course. If you already have a 92 (I went to a school that didn't have "A+", YMMV), there's no reason to increase your grades, and anyone else increasing their grade has the potential to devalue yours.
Note that this is fixed by just averaging your actual grades out of 100 to form your GPA, instead of mapping from a 0-100 range to an enumeration to a 0-4 scale then averaging the results.