The tax sale price is always the same. Instead of “bidding up” the price, people “bid down” the percentage interest they will get in the property. The bidder who offers to buy the least percentage interest wins. Many online tax sale auction sites allow you to set a minimum bid. Your public bid starts at 100% and goes down in response to other bids. 

IMPORTANT: The percentage interest is the ownership interest you may acquire if the tax sale is not redeemed or annulled. If you bid 1%, you are bidding to own 1% of the property if the tax sale is not redeemed. The tax debtor will still own the other 99%. It is possible that a 1% ownership interest will be worth less the tax sale price.