I think you have had some unclear advice, there is a difference between what BANKS require you to deposit (often at least 20% now particularly if you are a first time buyer) and the amount you have to pay on the day to the Auctioneer /Agency upon the fall of the hammer to secure the property, this is often 10 % BUT this is not mandated by law, it can vary, the exact details for each Auction will be in the Auction Terms and Conditions and these are available before the start of the Auction, so you need to have made arrangements with your bank if you intend to buy at Auction for them to pay the deposit that day
If you go to the REAA they have a range of guides you can download different guides to help you.
http://www.reaa.govt.nz/ForLicensees...ed-guides.aspx