Craps Need detailed real use of explaination of Buys

I understand the comissions, payouts and when they win and lose. What I don't understand is the real world use. Most casinos have the lowest chip of $1. I play $5 tables. So I don't understand how the rounding, and betting works. I want to know what are my payouts going to be if I bet any whole number between 5 and 25 dollars. Also I've heard about paying the commision up front, so what does that mean. Please I need real world in depth examples. If you are a craps dealer then please let me know what you do.