Bid increments go up to $1 starting at $25.
eBay only *attempts* to make the winning bid a full increment above the next to highest bidder. Sometimes, because of maximum bid limits, that's not possible. Remember, minimum bids are measured from the price *showing*, not someones max bid. You CAN win by less than a full increment. There can even be a tie for high bid. (earliest bid wins a tie)