Your $99.99 bid did not show up as $99.99. It showed as 1 inclement above the 2nd high bidder at the time. Your $99.99 bid was hidden. The bidder with the $100.01 bid outbid you by luck. He was required to bid 1 increment above the bid that was showing, not the hidden bid. He just happened to put in a bid that was 2 cents higher than your maximum, $99.99, and therefore became the high bidder.