i think its total payment.
10% might sound heavy but its much better than the going rate for transactions under $2.
right now paypal is currently the cheapest rate of all the services i know, and they take a commission of something like 3% PLUS 30 cent minimum. its the minimum that kills you for such low payments, and paypal is much better than most. some of the shareware services want to take like $2 minimum.
so the key to micropayment being good for receiver is to reduce the minimum. since the micropayment is "5 percent plus 5 cents per transaction", thats pretty darn good.