Are big supermarkets killing the food chain? A SPLIT second is all it takes to decide who to blame when you feel you're paying too much for your groceries. As you swipe your card over the "tap and go" reader at the self-checkout, a robotic voice is certain to remind you who is raiding your savings. It may even thank you for it. The name of the culprit should be no surprise: now that Australians spend about $80 billion a year at Coles and Woolworths, the two big supermarket chains are sure to bear most of the customer grievances.