Idk about you, but I haven't been asked to tip at my grocery store one time. I also shop at one that does cost a bit more but also does pay a bit more than other local competitors. You could always cook at home.

I also do tip food service on the rare occasion I patronize the business, which is another way. While you're still supporting the scummy business you don't also have to feel high and mighty about not tipping the exploited worker while doing so, you can just tip them instead.