The bid increment is the minimum amount a bid can be raised each time a new offer is submitted, it is determined by the value of the most recent bid.
For example:
Bidder 1: $210
Bidder 2: $230
To continue bidding "Bidder 1" must enter a bid which meets or exceeds $230 + $12 ($10 minimum) = $242

Because there is a second high bidder incentive offering a 10% bonus then the increment is minimum half of the bonus for the top bid:
$50 + $2 ($10 minimum) = $60