It's not a fixed tax where there is the same rate everywhere: when you check the tariff table, you can see that there is a different rate for each item (e.g. 9.4% for Cotton Jeans) and then it says in Chapter 99 that you pay "9.4% + xxx%" where xxx is the special rate for the country.

So it's xx% that goes on top of a rate defined by the type of the item.