Hi Prince,
I would recommend to control the tax determination by order types. Tax determination is also performed during invoicing, here you have an invoice document type but not a sales order type. And think of other document types you might use, for i.e. consignment deals or return orders.
SAP in standard distinguishes between domestic and export tax determination based on document data, i.e. by comparing the delivering and the receiving country. You have this information in the pricing structure KOMK.
For instance, have a look a pricing requirement routine 7:
Best regards,
Oliver