外国人です。I'm a Foreigner.コミュのSocial Insurance/Kousei Nenkin/Juminzei/Tax

Friends I am completely at a loss at how all the above are arrived at.
I see huge deductions on all of the above when I get my payslip and there is no one who is able to give me an convincing answer on the above...
even the Kuyakusho..
Is there anyone who wud have a excel macro or formula through which Kosei Neknkin, Taxes, Social Insurance , Inhabitant Tax and Unemployement insurance..

Specially for foreigners ..who plan to go back to thier country after a while ..the kosei nenkin does not make sense (except for americans and few other countries), if you are paying taxes...why the F@#K you have to pay inhabitant taxes..

Infact I have started thinking of leaving Japan because of all these stupid deductions which no one is able to explain to me..if there is an convincing answer i don mind..but you know it is like those internet connection and telephone connection campaigns which I bet most of us still dont understand