The GST is imposed on the total of the bill including stamp tax, levies, and carbon tax. There are some exemptions to larger business and even some taxpayer funds to offset impending closures of other business, but when all the dust settles the end user pays the tax plus the GST.
Combet lives in a parallel Universe full of compulsive-obsessive people tugging at their trouser legs. Oh, and now hates The Greens who's policy in partnership with Labor he trumpets.