Sometimes working with money can be difficult to understand for young students because it is an abstract concept. When you show them different ways to make those connections, it gets easier and becomes less abstract.
Making fair exchanges with money is difficult unless students have concrete experiences with it. Here is one way to make fair exchanges. It's like the rolling to 20 game, but you have to keep exchanging fairly and with the makeshift base ten blocks. The blocks are cut and hot glued or super glued together. If you look closely, you can see the small "n" written (for nickel) on the base ten block that is a group of five. When I tried to skip a trade, I was encouraged to keep making fair trades correctly. You can see that they're glued together in groups of 2 tens and 5 ones and can be fitted together like a puzzle to make groups of fifty and one-hundred.
Anytime you can make learning fun, students learn!