“…the average person treats a price ending in .99 as if it were 15 to 20 cents lower.”
The tendency is called left-digit bias, when the leftmost digit of a number disproportionately influences decision-making. In this case, even though the real difference is only a penny, research shows that, to the average person, $4.99 seems 15 to 20 cents cheaper than $5.00 – which results in selling 3 to 5 percent more units than at a price of $5.00"
This trips you up so many times if you visit the US from somewhere else. The number of times I’d see a snack listed for 99c, have a dollar bill on me and then they ask for like $1.12 is higher than I’d like to admit.