I have fully described the need in https://bugzilla.gnome.org/show_bug.cgi?id=765375.

I could add that I have found a workaround for representing taxes in a way that allows me to choose whether my income statement shows net income and net taxes with payroll tax deduced from both, or gross income and gross taxes with no sign of payroll tax in the report. I do this by first accumulating payroll tax as negative income, then adding special year-end transactions, and finally choosing whether to do case sensitive filtering or not when I run the Income Statement report. This method, however, does not scale to the multi-step problem in general, and is probably specific to Finnish tax system anyway. I would prefer a properly automated, generic solution.