One of the misleading things about eBay is that you can win by less than the increment because eBay just looks at whatever price is actually displayed.
So, here's an example:
Scenario 1: Starting price is £15
Bidder 1 places a bid of $15
Bidder 2 places a bid of $655
On ebay, current price shows as $15.50 (because bid increment is 50c on this amount on ebay.com)
Bidder 3 places a bid of $700 and wins for $665
Scenario 2: Starting price is $15
Bidder 1 places a bid of $650, price shows as $15
Bidder 2 places a bid of $660
On ebay current price now shows as $660 (bid increment is $10 on value 500 - 1000)
Bidder 3 places a bid of $669 and loses - auction is won for $660
At least that's what I think happens !!