Donations together with MarketPress orders, let people choose an amount


Is there a way to a kind of donation solution together with Marketpress shop?
I was thinking to let the user add an amount they wish to add to their order, which they should go to a fundraising project.

Right now im using the fundrasing plugin where user can donate from site which working very well, but i want to take some money from other places like when people buying anyway they can add 2 USD to cart, that will go to the fundraising.

Is there a way to handle this?