Yes, you can analyze transactions for roundups from a linked credit card. All you have to do is add a checking account to fund those roundups.
Let’s say you add your checking account to your Changed App, and later link your credit card you use frequently for Changed to analyze your spending and round up transactions.
In this case, we would round up transactions made on your Credit Card and make Changed transfers from your selected checking account. We don't want to be adding to your debt, right?