Several counters, one stock
Each till is a separate login billing into the same stock, so what sells at counter two reduces the same figure counter one is looking at. The day-end breaks down per user — not out of suspicion but because a pricing mistake or a wrong payment mode is far easier to find on the same evening than at month end when nobody remembers a Tuesday.
Category margin, not just turnover
A supermarket can grow turnover while making less money, because the categories that move fastest are often the thinnest. Sales by item with purchase rate against sale rate shows where the margin actually is, and it usually changes what gets shelf space. Running that monthly is fifteen minutes that pays for itself repeatedly.
Stock across thousands of SKUs
Nobody counts a supermarket by hand, so the stock figure has to be a by-product of billing. Every scanned line reduces it and every purchase raises it, which keeps it true. Minimum levels on the fast movers give you a warning before a shelf goes empty — and an empty shelf is a customer who tries the shop down the road next time.
Returns, offers and discounts
A sales return credits the customer and restocks the item in one step so the shelf and the day's figures agree. Discounts are recorded rather than hidden inside a reduced rate, which matters when you later want to know what your offers actually cost you over a month. Staff can be allowed to discount up to a limit, or not at all.
Shrinkage, and where it actually happens
Every supermarket loses stock it cannot account for, and owners tend to assume theft when the causes are usually duller: an item billed at the wrong rate, a return restocked twice, damaged goods removed from the shelf and never recorded, or a mis-scan on a similar-looking pack. Recording damage as a stock adjustment with the reason, and closing the day-end per counter, separates those from genuine loss. Once the ordinary causes are removed the residue is small and worth investigating; without that, the whole difference is a mystery nobody can act on.