Why Didn't My Coupon Double?

Most of my local grocery stores double coupons.  From time to time, you will find that a coupon you used did not double.  There may be a few reasons so do your homework before you shop.  A coupon with a barcode that starts with a 5 will automatically double even if it says on it "do not double" or "do not double or triple".  The register will automatically double these but a cashier can manually override this if he/she reads it and adjusts it.  Coupons with a barcode starting with a 9 will never double.  You will find coupons like this in those "Blinkie" machines on the edge of the store shelves.  You know, the ones your kids love to pull out and wait for the next one to come out and pull that out and over and over again until you stop them!  Another reason your coupon may not double is that some stores have a limit on how many times a coupon for the same products will double.  For instance, at ShopRite, if you are purchasing 5 of the same product and you have 5 coupons for those 5 items, the first 4 will double and the 5th one will not because their limit is 4 doubles for the same coupon.  Stop & Shop is supposed to have the same rule but I have found that more than 4 will double.  Another reason is "there is no reason".  From time to time a coupon will not double and there is no logical explanation for it and you need to bring it to the cashier's attention so they can call a manager over to override it.