If you are the high bidder, you would win by only one increment, just as if you had bid on eBay. So if the 2nd highest bid is $43 and you bid $75, you would win for $44.
yes the sniper post a bid just high enough to win if the bid is $10.00 and your snipe is 20.00 and with no other bids you will win at $11.00 or so if someone has entered a bid of $19.00 then you win at $20.00 if the increment is enough.