Sales tax is expected to be added to the base price at the point of purchase, and the legislated tax rate is - ostensibly - public knowledge in whatever municipality the store is in.
If the prices on your items' shelf tags are accurate, as is legally required, you can sum up all your items' base prices, apply your locality's tax rate to that subtotal, and get an accurate total before hitting the checkout.
This article is about the shelf tags or labels being out of line entirely with the base prices the register pulls out of the system, which is obviously illegal basically everywhere. You can't display one price and surprise customers at the register with a different, higher price. This has nothing to do with sales tax added at the register and not shown on the tag.