That's not quite the way to stack percentages...
If I understand correctly, it works like this. The game throws a 1000-sided dice (since there are fraction percentages as well). If it comes less than 145 you get an Epic. If not, the game rolls again. If this roll comes less than 290, it's a legendary. If not, the game rolls a third time. This time if it comes less than 580 it's a rare. If not, it's a normal.