The last place I worked retail was using an inventory tracking program in command prompt that polled and updated once per day at closing. You could sell through standing inventory and the system would still show how many you had started the day with. If you really had to know how many of something you had on hand, it required either polling each register's sales data individually or temporarily closing them to fake daily closure to run a report on a SKU. It was not unheard of to waste an hour checking to see if the store or any others nearby had a single item for a single customer at a national chain.