Sum of Invoice line net amount (BT-106) = Σ Invoice line net amount (BT-131).
cac:LegalMonetaryTotal(xs:decimal(cbc:LineExtensionAmount) = xs:decimal(round(sum(//(cac:InvoiceLine|cac:CreditNoteLine)/xs:decimal(cbc:LineExtensionAmount)) * 10 * 10) div 100))