Congrats on the employment!
I don't know if I could do that kind of job or not. Handling anyones money except my own makes me very highly nervous. I don't know why but if anyone accused me of not giving them the right change or anything like that I would melt.
I would also probably be the worlds easiest mark for every scam in the world.
DR Elmore, I miss Jane too. 
Fortunately, a lot of the job, like adding everything up, is handled by computers. This store has screens that show everything that is being scanned AS it is being scanned, with a running total and any discounts shown in real time.
Any problems with a customer, the running order is to call over a manager, which makes sense. Takes a lot of pressure off of the cashiers.
Still, as with any clerical job, there are people out there who are bound and determined to make the clerk's life hell, just because they can. It pays to develop a thick skin. And the proper meds help, too.

No, seriously, if I weren't on antidepressants I wouldn't want to even think of attempting a job like this. That, and a few philosophical roots should help me through the rough spots.
For one thing, I know better than to take the nasty bits personally. These people don't know me from Adam (or Eve), and will generally be venting their own anger with the world in general. It happens.
Second, it's up to me to deal with each and every customer as they come to me. Each one is an individual, worthy of my respect and attention. And while some of them will be rotten as hell, others will be wonderful people. Those will deserve to be celebrated, and I intend to.
And I'm not going to be working for tips! Take a gander at some of the writings at
Waiter Rant, and you'll learn a lot about how some people can behave.
Now, as for scams, that's going to be something I'll just have to learn, and learn fast. Actually, I'm glad you brought the subject up, so I'll remember to ask my bosses about what they know.