A mathematical irritant

Why is it so difficult for some who create a store's or restaurant's price signs to understand that .99 cents is the incorrect price?  It should be expressed as 99 cents or $0.99.  In the '80s, I saw a sign on a restaurant offering breakfast for 99-hundredths of a cent.  For that price, the customer shouldn't complain if a plate arrives with with just one grape, one piece of cereal, or a barely detectable sliver of a fried egg.