The 10% tithe had a purpose in the Law of Sinai. One of the twelve tribes, the Levites, was wholly devoted to the service of God. That was their role, by birth: to collect the tithes and taxes, to carry out minor judicial roles, and to serve periodically at the Tabernacle/Temple as helpers to the Aaronic priests.
The other 11 tribes were given land and farms, but not the Levites. They were only given a few cities. And unlike celebate Latin Rite priests of today, Levites married and had children.
The tithe, then, was in part a means by which the other 11 tribes provided the financial support for the existence of the tribe of judges and religious administrators.
However, only so much of the tithe went to support the Levites. The rest of it went to support the poor. It was, in effect, a religious welfare tax.
But now consider the circumstance of Christians. The Temple is down. The Aaronic priesthood is gone. The sacrificial rites of the Torah, which were only ever for Jews in Israel, are gone. As Christians, we do not have a twelfth of our population designated by birth as priests and their servants.
The Church certainly does a great deal of charity work, which is similar to what the Levites did, but today the state itself is the primary source of revenue for support of the retired, the sick, the orphan, the aged, etc. So a portion of the old tithe has been subsumed into taxes.
Catholic doctrine is that there is no fixed amount, no tithe, but that Christians are obliged to support the Church. That is all. Christ never established a tithe. The early Christians gave everything they had, including, often, their lives.
So, bottom line, no tithe. There never was a Christian tithe. God only ordained a tithe for Israel, and we're not Israel and never were.