How tax on income/salary is used?

Dear all,

I am interested to know how income tax or salary tax that each individual Cambodian has to pay to the government tax and custom unit be used to improve social services. So far, I have not heard anything about how revenue, in particular from income or salary tax, was used whether to improve social public services (such as health service, education service or commune/sangkat works) or to provide pension to the payers when they are in retired age. I have many arguments with my colleagues with regards to the use of tax. To me, I still do not see any benefit in paying income/salary tax; while others said that the revenue in particular from income/salary tax was used to improve high priority areas such as physical infrastructure.

Please share me your thought about this and I would very much appreciate if you could share any related papers on this issue. :-)