Scanning Code of Practice is presently a voluntary practice used across Canada to ensure that the scanned prices of goods match the advertised or posted prices.  It applies to all items with a UPC code, except those with an added discount sticker price. 

retailcouncil.org/scanner-price-accuracy-code

It is voluntary in all provinces and territories except Quebec where it is the law.   Many retailers used to follow it, Walmart, Save-On,  Safeway, but no longer do so.  Without a mandatory requirement many stores can over charge without consequence as most shoppers do not pay attention to their purchases as they are being scanned.  I do and have personally been overcharged and had to seek corrections and reimbursement for the overcharged amount.  But I never see any action on the part of the store to correct the price in the system. 

With so many people in the low income bracket and prices continuing to rise, the present set up is unfair.  Big stores especially are seeing record profits. Consumers need more protection from predatory practices.