How to input supplier invoice for Importing Goods

Joe I have a question

Hi I have a question on how to input goods that are imported, the cost of the product is made up of various expenses.
Example

Item 01 cost US $ 10.00
Shipping Cost US $ 2.00
Import Taxes US $ 3.00
Custom Agent Fee US $ 5.00

So the new Cost for item 01 is US $ 20.00

So on my purchase order I input the cost for item 01 of US $ 20.00

so far I don't have any problems.

The problem is went the Custom Agent send me is bill.

On his bill he charges me for service US $ 5.00 plus tax
Went I pay him I have to retain 1% of the US $ 5.00 for local gob. payment at the end of the month.

The 1% is no problem because I set the Discount box to credit the local gob. tax account

My problem is went I input this invoice I'm duplicating the US $ 5.00 charge for Custom Agent Service, because it is all ready include in the cost of the product.

What Can I do on this case, I have the same problem with the Shipping Invoice.