Clicks Overcharging for advertised Items

This review pertains to the Clicks at Reservoir Hills Mall.. Purchased Omo 3kg Auto Washing Powder with a shelf price tag of R135. Paid at the cashier and admittedly did not cross check the till slip...but should I have a need to do so?? Later that day when glancing at the till slip I found that I was charged R145. My concern is that why on most instances these "mistakes" are made with the customer being compromised. When last has anyone been "mistakenly" charged less for an item? A R10 difference is maybe not life changing..but accumulative by the many "mistaken transactions" is a tidy sum to Clicks. Morally Clicks should provide restitution to the customers that have been overcharged, I would like to hear Clicks comment on this matter... I am definitely going to demand my refund the next time I am at the Reservoir Hills mall! Customers, please consider your options when choosing retailers of dubious reputation.