At the cashier checkout lane: After the cashier tells you the amount you owe, say you have a Healthy Food Shopping Card. have your card scanned before you pay. Any items marked with the "GreatForYou" logo, will be reduced in price by 10% right there at the register.
At the self-checkout: Scan all of your items then select finish & pay. > Select shopping card and scan your HealthyFood Shopping Card > Select your final method of payment and pay for your items.