Let's look at the flipside.

If a cashier short changes you and you do not realize it and left. Do you think the cashier would track you down and give you the correct amount? Do you think if you went back there at a later date, talked to the same cashier and the cashier would be able to give you the difference?

I don't feel bad for someone getting fired for not doing their job well. Should you blame someone else for your own mistakes? I think if you make a mistake, own up to it and accept the consequences. It's the downfall of American society to think everyone deserves a job whether they are qualify to do it or not.