ok
well in a very bold attempt to bring the post back on topic:
I think the game in general lets the user's perform 'discovery' of elements. Training speed, merchandise source ratio's, etc...
revealing the economic rates of Tax % drop off would be contrary to most other elements in the game.
So whilst I agree that it would be nice to know these rates and what causes them to drop off and by how much (ie: Whats the formulae), I think these are elements that user's should discover, talk about in forums, perform statistical analysis based on their own transactions and gather this info and share with the community.