I voted 10% but i think the poll is a bit off. Realistically it's probably more like 2-3%, i.e. just a few purchases, although there have been times when I've done a lot more (especially, using bitrefill, but also e.g. travel expenses). So I think it'd have made more sense to do 0, 1, 5, 10, 25, 50, 100 or something similar.