Item Charges on Sales Order completed by a purchase invoice

I have never managed to figure out if this is possible in Nav.

I sell Items to customer SMITH. I add an Item Charge called DHL to the Sales Order. It has a cost of £10 and a selling price of £15. Sales Order is then shipped (via DHL) and invoiced.

I then enter a purchase invoice against supplier DHL and do some kind of functions that lists the item charge of £10 and post the supplier invoices. I pay DHL £10.

I have been supporting Nav for years but I have never understood if this is possible


Thanks
Chris W