Is using tax money to open up a halal business halal
If your question is regarding using the income tax refund to start up a Halal business or to use a legal tax credit or benefit for that purpose then it is absolutely permissible as it is your legal and lawful money.
If your question is concerning committing a tax fraud and then using that money to open up a Halal business then that would not be permissible because tax fraud is illegal and it would not be considered permissible.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America