A progressive release of rather similar announcements from the four major Australian banks on their current best estimate of the cost of the proposed liability levy yields nuggets of data, but scant insight.ANZ, Commonwealth Bank, NAB and Westpac over the last two days produced estimates that sum to around $3.9 billion over four years, well shy of the $6 billion Treasury projected in the recent federal budget and based on a tax rate of six basis points on the wholesale liabilities and some other deposits of banks.With each bank's key officers and advisers having access to the otherwise still secret draft bill to implement the tax, outsiders can only guess that banks fared well over recent days in promoting technocratic analysis of a tax the industry guessed from the outset its government sponsors misunderstood.Big deal if there's intricacy in the modelling. Maybe scores of specialists have shown up Treasury for being under-informed.The only cell in the model that matters is the final total that matches the government's fiscal and political objectives. Based on the bank's estimates its easy to see the six bps levy being reset at nine bps.In Australia, in a banking industry nowhere near overcoming a toxic past, tax collectors and the new bank tax are both unavoidable.