Josie, you've hit the nail on the head.....no one wants to be bullied into a donation at the checkout after just spending a goodly amount of money on groceries.
One day at the checkout in Walmart.....the lady in front of me replied by saying, that she would be glad to donate, if the store would then take that amount off of her total bill.
Those huge stores should be ashamed of themselves.....they could well afford to make a donation to whatever charity they chose, for each patron going through their checkouts.
I too bought a Heart and Stroke calendar.....and am considering the $100. ticket as well. I/we donate to the local foodbank......and Salvation Army as well.
I insist on making my donations to whomever I choose, rather than having someone else make my choice for me.