I've been unable to use per-transaction tabs located on the last line of a transaction (e.g." ; :TAG:") as shown in Section 6.7.1 of the Ledger 3.0 manual for processing an automatic query.
By experiment I found that the reason my tag-query was not working was related to the location of the tag in the relevant transaction postings. The last-line tag location suggested by the Manual (at Section 6.7.1) did not work for me. But locating the tag on the same line as the transaction amount --- as suggested by the Manual for per-transaction notes at Section 6.6 --- DID work.
------------ DID NOT WORK ----------------
2011/09/03 SOME INTERNET SOFTWARE SUPPLIER
Expenses:Business:Office $4.70
Liabilities:MasterCard -$4.70
; :no-vat:
--------------- DID WORK -------------------
2011/09/03 SOME INTERNET SOFTWARE SUPPLIER
Expenses:Business:Office $4.70 ; :no-vat:
Liabilities:MasterCard -$4.70
=============================
The automated query that I am using subtracts the tax at a standard rate from the total sum of the transaction, adjusting the expense represented by the anonymous '$account' variable and crediting an account that records the total amount of tax I've paid in purchases from other suppliers. On some transactions, tagged "no-vat", however, I did not pay the usual VAT. This automated query takes care of the distinction.
= ^Expenses:Business and (not %no-vat)
$account -0.090909091
Liabilities: VAT Paid 0.090909091
Best,
Peter