It’s funny that you mention that. We just released an extension today that helps with micro donations I’m not actually sure if this is what you’re looking for. It’s not what your describing, but if it’s all about giving to charity, give it a look.
“This web technology (API) harnesses the power of micro-donations by inviting your customers to round up their change or add an extra dollar to their balance for donation to a charity of their choice. We then aggregate these donations and thousands more from other e-tailer partners in our network, and distribute them to the corresponding non-profits. “