Natural foods grocery chain Whole Foods has plans to integrate Square’s iPad cash registers into its stores, with a few of its locations already implementing the devices. Whole Foods has signed a deal to put its iPad-based payment systems inside US grocery locations, where they will be used at counters that sell ready-to-consume products, such as pizza, sandwiches, and beverages, for the purpose of supplementing conventional checkouts. Customers will be able to pay for ‘quick purchases’ at the cash register with credit and debit cards, cash, and the Square Wallet smartphone app (in some locati…