Only one tax total without tax subtotals MUST be provided when tax currency code is provided.
PEPPOL-EN16931-R054pxs-taxdata:TaxData/pxs-taxdata:ReportedTransaction/pxs-taxdata:ReportedDocumentcount(cac:TaxTotal[not(cac:TaxSubtotal)]) = (if (cbc:TaxCurrencyCode) then 1 else 0)