Double,triple check till slips

I advise the customers that shop at Dischem to double check even triple check their till slips before leaving the store. I have on two separate occasions, this week, been overcharged for items that were priced differently on the shelf. Upon asking the reason for this, the cashier supervisor informed me that the pricing on the system is done by head office and cannot be rectified in store. The matter on both occasions was rectified by the supervisor by doing a manual overide on the system. Management and IT need to up their game as many people don't check till slips assuming the pricing is always correct and Dischem benefits from this.