I cashier, and I did some looking around the internet and fit day gives you a place to enter your info and see how much you burn an hour. Under occupation I found 'Standing - Light' which fits stuff like cashiering (which I do), bartending, etc. This should work for your job as well. The link:
http://www.fitday.com/webfit/exerciseinfopage.html
With my height and weight I burn 120 calories an hour that I cashier

Not bad, since I usually do at least 25 hours a week. It's like being paid to exercise