Hypothetically if you incur 10,000 transactions per year with the max rounding up of $0.04 per transaction, you're out $400.
This doesn't make a huge impact to individuals, but it absolutely will to large volume businesses.
If a store games prices to charge 0.2% more on a million transactions it's still 0.2% for them. Except the rounding on multi-item purchases isnt predictable so it would probably take a miracle of data engineering and behavioral science to hit 0.1% benefit on average.
Meanwhile stores are using 30% off coupons and buy on get one free to get people in the door, whilst hiding double digit price increases.
Worrying about the two pennies is stupid on either side of the transaction. Don't listen to the professional complainers.
No CEO is rubbing their hands together salivating over the idea of 4 cents per transaction. This likely won’t even show up on an earnings report because it’s literally going to be rounded away.
Also even if a business rounded up every transaction, the expected benefit is 2 cents per transaction vs fair rounding, not 4 cents.
I would expect many businesses to implement ceil()-flavored rounding.