The amount of cash that a bank keeps on hand in it's vaults and registers depends on the size of the bank and their daily or monthly transaction amounts.
Small banks keep between $20,000.00 to $50,000.00 in cash on hand in their vaults and registers.
Larger banks may keep between $200,000.00 to $500,000.00 in cash on hand to do their daily check cashing, cash loans, etc.
Most of the cash that a bank has on hand is actually in the vault and not in the teller's register.
So you might only get $2,000.00 to $5,000.00 at most when robbing a bank.
Also when a person robs a bank the teller actually slips a dye package in with the money that goes off and dyes the money as well as the bank robbers hand when they reach into it.