As for the rounding, just add .49 to the math. If the fixture divide out even, then it won't round up. if the fixtures divide out to x.01, adding this will get it to .5 where it'll round up. The schedule and parameters are set to integers, but this works even inside of that.
Let's say on one floor, I have assembly and business use groups. I can calculate the occupant load for each use, and my nested families will tell me exactly how many fixtures I need, for each use group.
I haven't been able to find a good way to automatically give me grand totals of required fixtures per use group. Have you been able to do this?