If I’m in the checkout at a business, say McDonald’s or Walmart or Kroger or whatever, and they ask if I’d like to round up to donate to some charity, I usually say yes. But should I be doing this? I heard somewhere that I shouldn’t because they can claim that as a donation from them which contributes to them paying less taxes or something, I’m not sure if that’s 100% how it works but I figure that it benefits them somehow or why else would they do that?
That is absolutely false.
Corporations can only donate on your behalf, so they get no tax benefits whatsoever. They cannot claim the money you donated as income nor can they donate it under their own name. The only thing they can do is use it for PR and tell the public “they helped raise $x for this cause”.
That said, if you donate a non trivial amount to charity, you should do it directly with the charity so you can get a tax receipt and write it off on your personal taxes.