I think it is just a matter of time until all the person at the register has to do is put the money tendered into the till and press a button for a graphic display of what to give back. The cost of installing such capability will become minor compared to the losses from not having it.
Every major restaurant chain is eventually going to rely on electronic transactions for more and more of their business. If you talk to someone in the corporate management of one of these companies, they'll tell you that one of their primary goals is to drastically reduce the company's exposure to losses related to the handling of cash on the premises of these restaurants (incorrect change, theft, etc.).