eBay style auctions

Hello,

Is there a way to make the auctions eBay style. Right now, when someone enters a bid, it only increments the auction by $1. I would like it to increment by the amount that the user entered.

For example, if someone is selling an item for $20, and I bid $25, it will change the price to $21. I would like it to change the price to $25, similar to how eBay does it. Is there a way that this can be done?

Thanks.