The problem still isn't solved. I had fresh instalation of 1.5.2. Whit the orginal Product.php I have default price 100 (with 8% tax.). When I add 40% discount to this product i get 59,99 but only in cart, in product price column. The price of unit display corect and the price of whole cart is also corect.
I replace Product.php from this topic and after that all prices was wrong whit amount 59,99.
I was trying whit rounding in code some prices but it works whit one product, but when i multiple amount of product the price again miss about 0,01
------------ UPDATE ------------
I solve my problem for now (i need to test this solution if it dosn't mess other thing).
I figured out that maybe the price is rounded to fast and i lost 0.01 from price during that proces. So i just add in classes/Product.php in function priceCalculation (2479 line) at the begining:
$decimals = 6;
Just only this litle line and solve my problem. Dont know if it works for other similar problem.