Exchequer will only apply the tax rate from the parent customer account if it is using taxcode A, D, E or Z, otherwise the transaction line will use the stock VAT code.
CRM will always use the ledger's taxcode when creating a quote. As such, we want to ignore any non-ADEZ tax codes from ledgers in CRM, so our solution is to hardcode that listinto the Exchequer ledger import to ignore any other codes.
Some customers have a bespoke Exchequer plug-in written by Xperience that allows the account tax code to always overwrite the stock tax code, and to support this we have written an AME to import the "other" tax codes, and set the CRM system option to ignore sledger_taxcode (to stop core integration removing the non-ADEZ codes).
This could simply be moved into a toggle in the CRM to determine whether the CRM (or the integration files) only use codes A, D, E and Z, or no restrictions.