Amount value precision

[David Goodenough <david.goodenough@broadwellmanor.co.uk>]

Currencies have natural precisions, so in the UK I can not instruct a bank to make a payment with more than two decimal places (i.e. pence).  Banking transactions are not the purview of UBL, but rather ISO-20022, however documents such as UBL Invoice and RemittanceAdvice document so include amounts that will have been transferred by some banking interaction.

Prices however can be set to more decimal places than a banking amount would allow, and it then rounded once the amount is calculated.  For instance last month we sent 81,400 litres of milk for which we were paid 30.672 pence per litre, or 0.30672 GBP per litre.

Are there any other objects other than the PriceAmount in a Price and the Amount in a PriceExtension which should not be constrained by bankable precision?

Has anyone (PEPPOL for example) come up with a set of rules as to which UBL Amount fields should be rounded to the relevant currency precision, and which can have more decimal places?  Does anyone know of a good reference for such decisions?

This is obviously not a UBL design problem (although it would have been nice if there were two different Amount objects, one for a bankable amount and one for a calculable one, but it is too late for that now) but an implementation question.

Thanks in advance