Your argument that income taxes are not definite and hence cannot be paid with sales revenue is not valid.
The light bill is not definite either. Nobody knows what it'll be until the bill comes. Nobody knows the copier payment ahead of time either.
So how is the timing of knowing the exact amount due for income tax, or the light bill, or the copier bill related to whether the expense can be paid with sales revenues or from some still yet untold place you haven't disclosed?
Light bills are based upon a rate which is known before hand as are copier costs. Though I know you don't like it they are easily calculated because you know all the variables in the equation. You know the amounts the rates are applied to thus the total bill.
You do not know if there is a profit until the accountants do their work at the end of the year thus you do not know the income tax. However, that has not had the slightest effect on the determination of the price of a product as have all other costs.
It is not sales revenue which determines whether a profit is earned or tax owed. One must have the cost picture completed before profit, a residual, is known. Let's say you owe no I.T. on sales of 1 billion then the next year sales double to 2 billion. You still cannot say whether there is any profit or tax just from that information. (Although I never said that I.T. "cannot be paid with sales revenue" in any case.)