A cash register, sometimes called a till or automated money handling system, is a mechanical or electronic device for registering and calculating transactions at a point of sale. It is usually attached to a drawer for storing cash and other valuables. A modern cash register is usually attached to a printer that can print out receipts for record-keeping purposes.

An early mechanical cash register was invented by James Ritty and John Birch following the American Civil War. James was the owner of a saloon in Dayton, Ohio, US, and believed his employees were embezzling by pocketing cash from customers or from the store's cash box. His solution was a machine that would record each sales transaction, producing a total at the close of the business day that could be compared to the amount of money in the till and the amount left over from the previous day, to determine if any was missing.

After being inspired by a machine on a steamship that counted the number of revolutions made by the propeller, and with the help of his brother John, James Ritty invented and patented his first machine, the Ritty Model I (also known as the Ritty Dial) in 1879. He then went on to produce additional models, including the "Incorruptible Cashier".

Early registers were entirely mechanical, and did not print receipts. The employee was required to ring up every transaction on the register, and when the total key was pushed, the drawer opened and a bell would ring, alerting the manager to a sale taking place. Those original machines were nothing but simple adding machines. For example, the Rittys' patent application filed in 1879 for their "improved cash register" describes the device as follows: "The machine consists, essentially, of an inclosed case or frame provided with an index dial and indicator operated by a system of levers or keys and connected with a series of co-operating disks marked with numbers on their peripheries, a row of which numbers are disclosed by a transverse opening or openings in the case to show at a glance the sum-total of cash receipts."

Since the registration is done with the process of returning change, according to Bill Bryson odd pricing came about because by charging odd amounts like 49 and 99 cents (or 45 and 95 cents when nickels are more used than pennies), the cashier very probably had to open the till for the penny change and thus announce the sale.

Shortly after the patent, Ritty became overwhelmed with the responsibilities of running two businesses, so he sold all of his interests in the cash register business to Jacob H. Eckert of Cincinnati, a china and glassware salesman, who formed the National Manufacturing Company. In 1884 Eckert sold the company to John H. Patterson, who renamed the company the National Cash Register Company and improved the cash register by adding a paper roll to record sales transactions, thereby creating the journal for internal bookkeeping purposes, and the receipt for external bookkeeping purposes. The original purpose of the receipt was enhanced fraud protection. The business owner could read the receipts to ensure that cashiers charged customers the correct amount for each transaction and did not embezzle the cash drawer. It also prevents a customer from defrauding the business by falsely claiming receipt of a lesser amount of change or a transaction that never happened in the first place. The first evidence of an actual cash register was used in Coalton, Ohio, at the Miners' Supply Co.

In 1906, while working at the National Cash Register company, inventor Charles F. Kettering designed a cash register with an electric motor.

A leading designer, builder, manufacturer, seller and exporter of cash registers from the 1950s until the 1970s was London-based (and later Brighton-based) Gross Cash Registers Ltd., founded by brothers Sam and Henry Gross. Their cash registers were particularly popular around the time of decimalisation in Britain in early 1971, Henry having designed one of the few known models of cash register which could switch currencies from £sd to £p so that retailers could easily change from one to the other on or after Decimal Day. Sweda also had decimal-ready registers where the retailer used a special key on Decimal Day for the conversion.^{[citation needed]}