Sick of Constant over billing

If you shop at Pick n Pay beware they are notorious for displaying a price on the shelf and then overcharging at the till. On the 27th March I bought a 7kg sack of potatoes - shelf price R34.99. When I got home and looked at the slip it had been rung up at R39.99! That is 18.29% above the shelf price. To get a refund I would need to go into their store and face the indignation of complaining be treated as a ***** and to boot waste my time - probably a good 15 minutes based on numerous previous experiences as they go into the depths of the store to locate the offending barcode or marketing material on the shelf and take the scenic trip back (time, speed etc is of no importance) and petrol for this experience!