Clerks are typically required by their employer to say or push things at the register. They are fine (and probably relieved) to hear you say no thanks.
I hated this when I worked retail. We had a number of things we were supposed to push at the customer, opening a store credit card, donating money, etc. I always felt like I was 1) annoying the customer trying to force something on them they didn’t want and 2) holding up the line going through my spiel.
I tried to judge the customer and say whatever I had to as quickly as I could. If they didn’t seem interested I was happy to move on, but if there was a manager within hearing distance, I was forced to do the whole thing. We would get absolutely beat down if we didn’t. They’d even write you up if they caught you not asking the customer. I was a really shy teenager. I hated it probably more than the customers did.
On the other hand, a quick do you want to round up, doesn’t bother me at all. I figure I can do that easily, and if each person just gives a tiny bit, it goes a long way for that organization. I don’t donate to get brownie points, or so I can write it off on my taxes. I don’t think that’s the right motivation for giving. I do it because I want to. There are certain organizations I care about I will give a larger donation to throughout the year, not through a store, but direct, so it doesn’t bother me to give these smaller amounts to places I wouldn’t make a larger donation to.
The only time I’ve ever contributed a larger amount at a store is when the local bookstore asks us to buy a book to donate. Reading is something I’m passionate about, and I like the idea of that and am happy to do it. They are always donating Dr Seus books, and they let you pick out the specific one you want to give.
But I enjoy volunteer work and working with aid organizations. I was an Americorps member when I was younger, and I’ve seen how donations, especially to grassroots organizations can really help. I’ve also worked with many different nonprofits over the years, and even at my current job, I am in charge of our donations which is a part of my job I really enjoy. Also, my sister is an aid worker in Central America, and I’ve seen her struggle to get donations to fund her work. So I’m probably not the average person being asked.