SUPERMARKET DISCOUNT CARD

I did something like this for a customer in AK,

how it was setup is have the customer fill out a form of some kind(customer created this) and create them in system as a customer and assign that customer priceA(in your case you could simply assign them a 5% discount) when you assign the customer to the transcation they will be given the discount of 5%(the advantage of doing a priceA is that you can give discounts on items that you want and items that dont have special discounts wouldnt be given, A second advantage of doing the price A is if something goes on sale the customer gets the lower of the 2 prices not a combined discount like they will get giving them a blanket 5% dicount, also they would print on say a shelf tag if configured correctly).