I used to work fast food and retail, both which forced employees to ask customers to donate at the till. We hated doing it. It is awkward for both the customer and the worker. I would get anxiety when donation drive time of year would come round, and I’d feel relief when the customer either just said no or yes, and didn’t yell at me for asking. The cashier REALLY does not care if you donate or not. And the cashier usually does not make your food, it’s usually someone else doing the cooking, and the cooks aren’t paying attention at all to whether you donated or not.