I tryed to be as simple as possible assuming that calculations were made separatly in different functions (programmer here). Anyway, tariff is a tax collected by custom office, payed by importer, included in final price that customer pays for the product.
That’s quite inaccurate. Many of these taxes are not additive but multiplicative:
Retail price = ((Purchase price + international transport costs) * tariff + national transport cost) * profit margin * sale tax
In other words, it’s even worse than you wrote.
I tryed to be as simple as possible assuming that calculations were made separatly in different functions (programmer here). Anyway, tariff is a tax collected by custom office, payed by importer, included in final price that customer pays for the product.