Usage example:
var invoice : Invoice = ...;
var productNet = invoice.productSubTotal.netPrice;
var serviceNet = invoice.serviceSubTotal.netPrice;
var grandNet = invoice.grandTotal.netPrice;
var grandTax = invoice.grandTotal.tax;
var grandGross = invoice.grandTotal.grossPrice;

# tax breakdown
for each(taxItem : TaxItem in invoice.grandTotal.taxItems) {
var tax : Money = taxItem.amount;
var taxGroup : TaxGroup = taxItem.taxGroup;
var rate : Double = taxGroup.rate;
var caption :String = taxGroup.caption;
var taxType :String = taxGroup.taxType;
}