How do I determine the percentage of the tax? I can only say “I want income to be this high”, but how do I know what the percentage of the taxation is?
Is it 30 % income tax? 50 %? What is it?
ah there is no way to know, its just a gradient between low and high. You can separate luxury goods taxes if you want to penalise the rich 
The taxation area is one I’d like to expand upon in future
I agree that taxation is one of the areas where the game could be improved. I would love to see the option to select what type of tax would you like to have in a country - a fixed rate, a progressive tax or a mixed approach. Also, it would be nice to have exclusions in the sales taxes (like a 0% tax for books or medicine) that would affect literacy, healthcare and so on.
Yes it seems that tax rates in real life are complicated. No matter what though it would be impossible for a videogame to simulate the tax system perfectly. For eg. In Canada they give you relief when you do your taxes if you were paying tuition at some University and that depends on how much income you make as well. There are so many “variables” in real life that affect taxes that it would be impossible to implement the system perfectly. However having a system where you can select between progressive, flat, the different tax brackets, etc. would be nice.