Autobids (for an auctioneer without an increment table or with non-dynamic increments) can be any amount, meaning they do not stick to the bid increments set for that item. A user can place any bid, regardless of whether it adheres to a value that would on an increment. So how does the bidding compensate for this? 

Take the scenario as follows:
Bid increment is £30. One user has an autobid of £372 and the other user places a bid of £355. The autobid comes into play so the current bid is now £372 with the autobidder. The next bid will then be £402.
So generally speaking, the autobid kicks in regardless of whether it is less than the next increment or not. And the next bid is the autobid + increment.

Here's another example:
Bid increment is £5. UserA has the autobid of £52, UserB bids £50. The current bid jumps up to £52. The next bid for all users is £57 (i.e. autobid + increment).

When a user tries to place a maxbid that is lower than the next increment, they will get the following error:

Unable to place bid. It is not higher than the current highest bid plus the bid increment. Please check the price and make a fresh bid.