Though I don't know the actual percentage I can say that the citizens of a country in Simcountry do pay taxes. Of course the more citizens you have, the more taxes you will collect. We cannot change the tax rate that the citizens pay though. However, with higher overall employment rate and higher income for the workers, you do collect more taxes. I believe government and corporate workers in your country pay taxes. You can adjust the salary level of government workers by clicking Departments -> Labor -> Salaries of government workers. Be sure to keep the corporate and government workers salaries within the same range of one another.
Avoid setting these salaries at a very high rate in an attempt to collect lots of taxes because their salaries are being paid for by your corp's and your country's budget. It seems like as a rule of thumb the best salaries are in a range of 200 - 600. It depends completely on your style of game play thoug