All bids on eBay use automatic bidding. It is just that if you only place bids for the MINIMUM amount, eBay has nothing left to use for automatic bidding. So you could say that by nibble bidding, you are effectively turning off automatic bidding.
But why would you want to do that? Do you like to lose?
It's been turned on since eBay was invented, and you can't "turn it off". If you don't want eBay to bid for you, just bid the minimum increment. But only do this if you don't mind being repeatedly outbid the instant you click the "Confirm" button.