Father Raniero Cantalamessa, Preacher to the Papal Household, discusses Christian financial obligations to the state in his Gospel commentary at Zenit.org:
Paying appropriately levied taxes is for the Christian (but also for every honest person) a duty of justice and therefore an obligation of conscience. Guaranteeing order, commerce and a whole series of other services, the state gives the citizen something to which it has a right for compensation in return, precisely to be able to continue these same services.
The “Catechism of the Catholic Church” reminds us that tax evasion, when it reaches certain proportions, is a mortal sin equal to every other grave act of theft. It is stealing, not from the “state,” that is from no one, but from the community, that is, from everyone. Naturally, this supposes that the state is just and equitable in imposing taxes.
Read his full commentary here.