Often with small-dollar items, the exact amount of money is relevant. I might have a $5 bill, but not have $5.39. So if that item that says "$4.99" on the price sticker costs $5.39 when I get to the register, that is just a nuisance and a waste of everyone's time.
And for what purpose? I can't believe that retail outlets don't already just price tax into the stated price.
Are they concerned that people are going want to shop elsewhere and pay the same amount of money but also go through more nuisance and do more math in their head along the way because they prefer to initially see a lower price?