No dollars go to Garage Games becomes Garage Games doesn't and never has charged royalties for using their engine, and no dollars go to taxes because Oregon has no state sales tax. Every April, he declares the income he made off the games (an LLC is not treated as a separate entity for tax purposes) and then a portion of that goes to the government when he fills out his 1040 or whatever, but this is not assessed per purchase. So for every purchase he gets $20 less bank and currency conversion fees, if applicable.
We have no idea how much of the money would go to Valve because all of the publishers have to sign a NDA, but we can assume that this fee is a percentage and not a flat rate, and is probably less than 25%. It's also probably individually negotiated per company as part of the contract, so one company might pay 11% while another pays 12%.