Small businesses can use POS systems to track inventory, process payments, and perform other business functions. As a result, a merchant's POS provides receipts, adds in sales tax, accounts for promotions, and completes sales transactions. A number of payment processors, such as Square, offer proprietary POS systems that include terminals, cash registers, and card readers. Some payment processors also offer POS bundles. Businesses can process payments using their computers and mobile devices with credit card processors that integrate with third-party POS systems or program existing POS systems.