How much money is the change ?

  If you work in a store or shop, the cash register will calculate the prize the customer must pay, and how much change he or she should get.

But you must hand the right amount back, or you will be in trouble - with the customer or the manager, or both.

The buttons can 'stick' a bit - the display at each sort of coin tells how many of that sort you will give back to the customer.