All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
There is no harm in working in a governmental sector if one is not involved in doing what is forbidden in such a job and does not help in it (what is forbidden), and there is nothing wrong with what he earns from it.
The fact that the government imposes taxes that may be unjust does not prevent working in such government and does not affect one's work. The sin falls upon the doer and the one who undertakes such injustice.
For more benefit on evading taxes, please refer to Fataawa 316597, 203644 and 129786.
Allah Knows best.