I don't have a problem personally (and my TLs haven't objected to the practice) of a guest splitting up their order so that they can earn the gift card on one transaction and then use it on the remainder of their items. As long as they are prepared for it when I get to them in my lane. I *do*, however, have a problem when they decide to do this after I've hit the total button, or if they try to do so in order to earn more gift cards.
I had a guest last night (posted in the TTOG thread) who bought over a hundred bucks in OTC medications. Advil, Tylenol, cold meds, etc. After I hit total, she finally started dragging out coupons from her purse, one at a time. Nearly another 3 minutes just to ring her coupons, and the guests are piling up behind her. When I gave her only one gift card with her receipt, she pitched a fit. By now, I had four more guests queued up, so I really didn't have time to deal with her. I pointed out that the coupon clearly says one per guest. She wanted to void her transaction and break it up. Nope, no way, no how. Even without the four guests behind her, I wouldn't have done it. As soon as she walked away from me, I was on the radio to my the service desk TM to warn him, because I had a feeling she was going to try and get him to "take care of it" for her. And then I called my GSA to let him know as well.