I work sort of as a back-up teller (long story). Not hard, but you need to be VERY accurate. I think most banks have a limit on how much cash you can be out before they fire you. Duh. As with any customer service job, busy times suck, and dead times are really boring.
Where I work, tellers perform a lot more than just standard Teller duties. Your bank may do the same. But I'll just list the basic duties here.
What teller's usually do:
1. Use computer/terminal to record all transactions.
2. Count money. Incoming and outgoing.
3. Process deposits. Checks and cash.
4. Count money.
5. Process check cashing.
6. Process withdrawals.
7. Count money.
8. Sell certified checks.
9. Submit Currency Transaction Reports to the Compliance Officer.
10. Smile at customers.
11. Smile at angry customers.
12. Count money.
13. Try to keep long line of customers happy by smiling at them.
14. Try not to look grossed out when a customer pulls cash out of...less accessible parts of their clothing. Smile.
15. Sell Traveler's checks.
16. Glance nervously at the latest police composite of bank robbers working in the area, and compare the pictures to people in the lobby.
17. Buy money from the vault when the teller drawer runs low. Count money.
18. Sell money to the vault when the teller drawer runs high. Count money.
19. Answer lots of customer questions about their accounts.
20. Balance teller drawer at cutoff time (typically 2 - 3 PM at most banks). Note that this time also happens to be when you get the most customers. So you end up trying to count all the money in your drawer while still making deposits and withdrawals.
21. Balance Teller Drawer at the end of the business day.
22. Lock up at end of day.
I have no idea how much our tellers get paid. I have heard of some banks paying $15/hour, but you need a college degree for those jobs. BTW, I think most banks will run your credit history and ask you a bunch of questions to determine whether or not you're likely to rob them.