why don’t you round up for charity

The thing is that they are. When you round up, that money becomes theirs. At the end of the donation period, they will donate all of your money and claim it as their own donations! They might even get a tax deduction and probably pay some number of employees who “manage” the charity out of the funds.

What everyone is missing here is that it isn’t just about knowing things, it is also about how you communicate those things and how you present yourself.