As far as the rounding is concerned, there are several "standard" ways of rounding. They are used in Math, but not as much because Math classes generally tend to use exact numbers, not rounded.
I have heard of the rounding method you describe and it probably works as well as any other I've heard of. The one I generally subscribe to is a bit simpler:
This sounds like it's perfectly reasonable, but there is a hidden problem: significant digits. You probably won't run into these until High School. The problem is there is generally some uncertainty in the last digit of any measured number. When in doubt, the last digit has an uncertainty plus/minus 1. So the number 10.5 is really . How do you round this using my method? You can't. (However we can just drop the last digit and say the number is , so we don't really have to worry about it, either.)If the number ends in a 5 exactly then round down. If there are any numbers after the 5 then round up.
Basically you'll see a lot of arbitrary definitions used in your Physics classes. You'll find that the rounding scheme is going to be the least of these, so don't worry about it too much.