Usually the drawer can be opened only after recording a sale, except when using a special key, which only senior personnel or the owner has. This reduces the risk of personnel stealing from the shop owner by not recording a sale and pocketing the money, in the case that the customer does not require a receipt and has to be given change (cash is more easily checked against recorded sales than inventory).
A cash register may be compulsory for tax purposes. The law sometimes also requires customers to collect the receipt and keep it at least for a short while after leaving the shop, again for checking that the shop records sales, so that it can not evade taxes.
Often cash registers are attached to scales, barcode scanners, checkstands, and EFTPOS or credit card terminals. Increasingly, dedicated cash registers are being replaced with general purpose computers with POS software.