Current thought
- Create Unit price + tax IShoppingCartCalculator - Calculate unit price and tax, store CartItemGUID and value in TaxSummary
- Register custom IShoppingCartCalculationFactory
- On external sync lookup Tax from TaxSummary
Thoughts?
I'm not overly keen on the use of TaxSummary, but think it would require significant customisation to add TotalTax to ShoppingCartSKU.