When there is a dynamic increment table in place (i.e. your increments follow a set table or pattern) then the autobids that can be placed are determined by those increments. 

When a user clicks 'Place Autobid' they are presented with a list of autobid amounts they can choose from by clicking on the dropdown list below: 

Here is the type of list they will be presented with, containing up to 100 options for the bidder to choose:

Please note: This does not currently apply to webcast pre-bidding.