I assume you mean fake money

. I've had two teammates who have done this. One had a bulletin board where each student had a little file for their name, and they put it there to keep when it was earned. It was kind of behind her desk so there weren't issues with kids walking by and messing with it during the day.
The other had little cups attached to the back of kids' chairs and she would put it in there, which seems like it would invite a lot more issues, IMO. Personally, it seems like a lot to manage and I wouldn't be okay with spending my own money on things for the students to "buy" with their money. I might consider it as a a last resort if I had a group that was incredibly hard to manage.