The id name of a tax class used in an order (such as zero or Z or whatever you have named them) should be an option as standard - at present it cannot be picked up by using meta name option even though it is a meta name in the order post -

If using the CSV export for populating an accounting software, the need to know what type of tax was used for each order is just plain essential - this is no doubt the case for many other users who are using this exporter for analytical or other purposes.