The winner of an auction will pay one bid increment above the next to highest bid. (with a few exceptions and can be less than a full increment)
Bidder A bids 240 on an auction with an opening price of 200. Current price on eBay shows bidder A the winner with a price of 200. (opening bid amount)
Bidder B comes along and bids 215. eBay will show Bidder A the winner at 217.50 (one increment above B's max)
Bidder C bids 275. eBay shows bidder C in the lead at a price of 242.50. (one increment above A's max)
You now snipe for $250. You lose to bidder C at a price of $255. (one increment above your max)
Get it?