Why doing good feels so bad

I tell myself every time I go into Safeway that I am NOT going to back down. I'm just going to tell her no, and be on my way. I can't keep doing this. I can't keep being guilted into this. I can't keep letting the mean old grey haired miserable lady at the checkout pressure me into 'rounding up to the next dollar to donate to breast cancer'. Ugh!! She gets me every time!! I go in there with a clear shopping mission and only bring enough money for just the things I need, maybe an extra buck or two if I need to buy a fat girl treat, but thats it. Anyway, it happens like this: I gather my goods, usually a bunch of bananas, some bagged salad and some tortillas and as usual the ghetto-fabulous Safeway I live near is always flooded with people and only three checkers to accommodate them. I file myself in line with the rest of the neighborhood and patiently wait my turn. Then the pressure starts to build. I tell myself, 'say no, just say no'. Think of all the money you would be saving if you just said no!! As I get closer to the register, I can hear the Grumpy checker, who never says 'hello' or 'how are you', but sure as shit asks the dreaded question "would you like to round up to help fight breast cancer'? To help fight breast cancer? Now is my rounded change really going to fight this disease? By giving up my 25, 35 even sometimes 75 cents, am I arming fighter cells with swords and shields to fight off those evil rogue breast cancer cells? I'd love to think that was the case. I'd actually would feel better about this donation if there was some sort of reassurance that my money was really going to fight this disease. Show me pictures of mastectomies, or of women who are bald and going through chemotherapy, show me more than pink sustainable shopping bags, or day old cupcakes with pink ribbons on them and prove to me that my hard earned money is actually fighting breast cancer! It may be rotten of me to feel this way, but I do. I need more than the scorn from the bitter cashier, or the guilt from hearing other customers cave to the dreaded question, I need more tangible assurance that what could be buying at least 1 tall black coffee at Starbucks is actually fighting breast cancer.