Tax Calculated at consolidated invoice level rather than asset level

We are having an issue with the tax that is calculated on the  OKL invoices.  When a contract is quoted to the customer the tax is calculated at the invoice header level.  However, when the invoice is generated in Oracle the tax is calculated at the line level not at the consolidated invoice level.  This causes some rounding differences between what is quoted to the customer (and signed) and what is on the invoice.

This causes the most problems with Direct Debits as the receipts are automatically created based on the invoice amount and then the funds are taken from the customers account.  We have had some situations where the customer has refeused to pay as the amount on the invoice is different from the amount the amount originally quoted.