Practice on a virtual cash register on Math-Play.com and MrNussbaum.com as of 2015. Both websites feature games that allow visitors to make change with online cash registers for free. Math-Play.com also features a cash register app for iOS devices.
Practice on a virtual cash register on Math-Play.com by clicking Money Games near the middle of the home page and then clicking Counting Money Game on the next page. Click Play to begin.
To practice on a virtual cash register on MrNussbaum.com, click Search this Site, type "cash out" in the search bar, and click Cash Out on the next page. Click Play to begin.