If there is a bid within 5 minutes of the auction closing, it will automatically be extended an additional 5 minutes from the last bid time. This will occur until there are no bids within the last 5 minutes of an auction closing.
This feature is in place to protect you, the registered user from being outbid by "sniper software". Sniper software is designed to watch the closing time of an auction and place a bid for the user at the very last second of an auctions closing. This leaves you with a very little chance of winning a bid.