The original price of the chips from Bitsyncom is 0.078, if you refund you get back 0.0817 so clearly steamboat is paying back some of his 10% markup. To be precise, around 47.4% of his markup, or as close as makes no difference to "half of the original 10%".
It could not be put simpler than this. If we get back more than the bitsyncom price. How can steamboat then charge us above that?
Its 5% his charges. nothing more..