It depends on the level of sense the attendant has; most are smart enough to realize that if it shuts off immediately that they need to restart it at a slower rate, but technically, they should end the transaction there. As for the other, no, there is no round off, when it shuts off yer done.
While that might be true for a percentage, most of this stuff occurs in the legislature due to the supermajority (guess which side), and they find out about it after the first of the year when all the laws take effect. I was at a gas station on 31 Dec topping off and mentioned the tax increase and no one inside the store knew about it, including the cashier. Everyone gripes after the fact about all the stupidity, and complain that they never got to vote on this. As our state rep and local radio guy says, "You do get to vote on these things, you just keep electing the wrong people to represent you."