Other forms: tilled; tills
The noun till means the same as "cash register." When you work at the store long enough, they'll let you operate the till.
When you pay taxes to your town, they go into the local till, or government fund, for community improvements. Till is also used as a verb, meaning to work the land, to get it ready for planting and harvesting. Till can also be used to mean "until," which makes things a bit confusing. So, technically, you could have a sentence like: Don't touch the till till you take the customer's money.