Okay, so it's easy I think. For the first 9 weeks to the whole semester everything is with quarters and dollars. It makes it easy and the kids get a good understanding of it. They earn money, spend money, and lose money. My rational: I get paid to do my job and being a student is their job so they get paid too.
I hang these posters in my room for them to refer to (at times I have to as well!!)
I have the rules:
Like I said my students really love this. After the second nine weeks or semester, depending on how well the class is doing with it. I change it up and add nickels and dimes. So it takes more to earn money but they learn all the ways to make a quarter. I wear an apron so my money is with me all the time and handy. That way when I am walking around I can just put give a student money whenever and where ever (hallway, another teachers' class....)
Here's me in my Home Depot apron. Although there are many, many, many cute aprons on etsy :)