Float keeps automatically rounding to 100mil

I have a float (yes, it has to be a float so math elsewhere works correctly), that, at a certain point in my code is set to exactly 99,999,999 and then converted to a string. I'm using number = 99999999 and then .ToString("#,##0") The inspector displays 1E+08, so it seems to be that any number close to 100mil is automatically set to 100mil. Any way to fix this?