I bought breakfast this morning and handed the cashier a twenty dollar bill. Have you ever noticed that there are two kinds of people? Those who know how to handle change, and those who don't.
The cashier handed me my change with all the coins on top of the bill, so when she handed it over to me, the coins slipped off the bill and on to the counter.
This problem is very easy to avoid.
To reduce the risk of coin-droppage, use two hands - change in one, bill in the other. Then, hand off the change to the customer. Crisis averted.