Actually, tithe is an Old Testament prescription that is no longer binding upon Catholics. The prescription for Catholics is the precept of the Church to “help to provide for the needs of the Church” in a manner that is for each person “according to his own ability” (CCC 2043). Although giving ten percent of one’s income to the support of the Church is a good thing, it is not required. All that is necessary is to support the Church in a manner that you are capable of doing so (which can also entail offering time and talent in addition to, or in substitute for, treasure).
Since the precept calls for supporting the Church, then that which you set aside in fulfillment of this precept should go to the Church. It can go to your parish, diocese, the Vatican (through Peter’s Pence), to a religious order, or to Catholic apostolates or charities. Such a decision is yours. Whatever you give to charity in addition to your support for the Church can go to worthy non-Catholic Christian and/or secular endeavors.
The Catholic Answers Guide to Family Finances by Philip Lenahan