Now Now kenashi, don't you dare take away my business! 
Anyway, for all those who wants to know your perfect tax level,
refer to the mini guide below(taken from WIKI)
Lowering your tax rate lowers the percentage of taxes each of your
citizens pay on their income but increases your population
happiness. The happier your population is the more money they will
make, so sometimes lower tax rates will earn you more money than
would a higher tax rate.
10% - 16% = +0 population happiness
17% - 20% = -1 population happiness
21% - 23% = -3 population happiness
24% - 25% = -5 population happiness
26% - 28% = -7 population happiness
---->Despite how 'angry' your citizens may get about the
amount they are paying, there are no other negative effects to a
higher taxation rate.
How to know
your ideal Tax Rate?
~Set your tax rate to 10% and see what your "Avg. Gross Income Per
Individual Per Day" is. Let this value be X.
Therefore
if 0 < X < 9 set TAX RATE to 16%
if 10 < X < 32 set TAX RATE to 20%
if 33 < X < 50 Set TAX RATE to 23%
if X > 51+ set TAX RATE to 28%
*IMPT* The only effect of your citizens being angry is a decrease
in happiness, and since happiness only affects income as long as
you're getting the most money you can, it's fine to keep the tax
rate the same. No matter how angry your citizens get, they will not
riot and there will be no negative effects.
Hope it helps somehow.
CHeers
