There is of course much bad teaching in the church regarding tithes and such, much of it because of hoe modern-day ministries get themselves in a position where they have huge and overwhelming overhead expenses, and the pressure of it all causes them to err in doctrine concerning financial matters.
The NT Christian is of course not under any such dead letter of the OT Law, such as the ORDINANCE (such as were nailed to the Cross) to tithe.
On the other hand, we who are in Christ were purchased with such a priceless cost, God's Own Son--not to mention the fact the God is the ultimate source of everything--that the Heavenly Father thereby believes He has the right to consider all that we own as being His. The first century, apostolic church knew this, and they liquidated their major assets and gave all the proceeds to God (gee, I wonder why they had such power to change their world).
We under the New Cov. are to be rather led by the (S)spirit, to learn and obey His moment-by-moment (V)voice, and obey. This takes experience and many failures ("who through reason of use have their senses trained to discern good and evil" [KJV]; etc.). Therefore, in regards to what monies we are to give, it is the amount that God's Spirit tells us at whatever time and in whatever circumstance He speaks.
"Today, if you [will??] hear His Voice, harden not your heart."
The above notwithstanding, since the new--and many a veteran--Christian cannot correctly discern God's Voice, then another Kingdom principle comes into play, that of using the things of the Old Cov. "as examples. . . ." (KJV), and it is generally wise to use 10% as a starting point, asking God by Faith to eventually show you a better way, and to correct you if and when you are wrong to give the 10%, or even anything at all at times. All things by the Spirit, but 2 or 3 "witnesses" are even better.
"It seemed good to the Holy Ghost and us, that you should. . . ."
Finally, all Christians, virtually/practically without exception, have still hiding within their heart the Love of money, the Love of this world, from which they need to be specifically and miraculously delivered--and which prevents them from walking in Love (1 Jn. 2:15b), which is required if we are to one day inherit eternal Life (1 Jn. 2:3-5; Lk. 10:25-28; 1 Jn. 4:16-18. Rev. 22:14; etc.). This remaining idol of agapao for the world will most always cause the Christian to make incorrect decisions regarding tithes and offerings and personal possessions.
The Good News: He offers more Grace, including the Grace of repentance for when we don't feel like repenting. Ask Him, in Jesus name, and believe, nothing wavering.
jim