As per Japan Duty, we need to calculate Tax as per Cart total.
So to fix complex Japan Duty issue:
1. We added a code in which we calculate total amount of lines related with a SalesTaxCode (CJapanDuty or GJapanDuty)
2. On the basis of lines total amount, we check for the tax interval for that lines related with SalesTaxCode.
3. This way we can do seprate calculation for both the SalesTaxCodes in the same Cart.
4. And each group has seprate tax calculation.