A lot of research has gone into this and for better or worse it works so well that any price not set this way is not getting the best results for the seller.
As it turns out there hasn't been a lot of research into this. There was research on it that is the goto but I believe it references old catalog sales only(like sears) and not in store.
Edit: it may be more like people view products with a decimal price as cheap and products with whole numbers as quality.