How would you respond if your boss yelled at you and accused you of stealing money?

You don't have to take being talked to so badly. I probably wouldn't quit, but maybe you and some others who agree with you should go to someone higher up than the one who is doing it and tell them how he is acting and that he is rude to the customers, maybe a talk with his supervisor will change his attitude a little.

Such it up, wait tell after the holiday , then quiet.
i would not respond to him. I would just do my job. Mind my own business.

For leaving: Accusation of theft is a serious charge. If he is accusing you directly, you must quit and consider legal action. To make a blanket accusation is insulting, but at least it isn't personal. Direct accusation is the only reason I would quit. Unless it is a matter of honor. If he seriously thinks that you may be stealing, and you are not, and legal action doesn't seem appropriate since it hasn't come down to a direct accusation, but if you are losing sleep, or are feeling belittled, or treated disrespectfully. Then leave. (I am leaving my job for this reason- I am being treated disrespectfully.)
Against leaving: If you need the money. Or, if you leave, would it appear that you are guilty? Do you need the job for a resume? If you leave before the holidays would you get a bad reference? Meanwhile, be not only carefully honest, but conspicuously honest- go out of your way to been seen to be honest.

It sounds like he shouldn't be in authority. If he were accusing me personally, I would not put up with it. Especially if I didn't need the job. I would go to the higher ups and let them know, then I would put in my 2 weeks. If the higher ups decided to persue the matter and did something about it and wanted me to stay then I would, (if I liked my job). But I think life is too short to put up with that sort of thing and depending on the circumstances, life is too short to go through a fight. There are times that the fight is worth it but sometimes it is just better to let it go, move on and live your life. You need to decide what it really means to you.

Is there an HR person/department you can go to, or a higher level manager?

When ever it gets like that its best to just go ahead and find something new, I've been working at home for over a year and I've been able to find some successful jobs working at home as an independent contractor, I got some information through this site and I've gotten a lot of help try visiting the site and give them a try, they may be able to help you out if your trying to build your own business, I know they've help me. :)
http://www.wahmjobfinder.com/livelonger

Do you by chance work at walmart??? this sounds so familiar...

It is actually at Walmart....