Giving false with certain answers

Hello,

I am having an issue with my formula. Certain values will give me the correct answer (A, B, C, D, F) but other values will give me a FALSE. For example: if I have 2341 pieces received and 32 pieces rejected, I will receive a false, however if I have 200 pieces rejected, it will give me a B.

=IF(F29>=99,"A",IF(F29=98,"B",IF(F29=97,"C",IF(F29=96,"D",IF(F29<=95,"F","")))))