omg i totally know how it feels, i was in the exact same situation. I had an 89.7 in calculus, but the teacher wouldn't round it up to a 90...wtf?! i got a B+ in the class =(
Yeah. That's always tough, to be that close to the next letter grade. It doesn't hurt to talk to your professor to see if rounding is an option. The worst response would be "no." I know that many of my profs specifically point out on their syllabi that a C is 70.00-79.99, B is 80.00-89.99, and so on.
Our pharmacology syllabus states "I don't round and please don't ask me to." What really sucked is that the normal range for a B+ is 87 to 89. This class was 88.0 to 89.9. I finished with an 87 and would have gotten a B+ in any other class.