I personally believe NT believers are to give MORE than 10% to the Lord's work. Not only do I believe this, we have personally practiced this for many decades now.
The tithe (10%) is an OT commandment, a reference point. In the NT 100% belongs to the Lord. In regards to "how much" of that 100% should be given back to the Lord, Paul answers, "each one must do just as he has purposed in his heart..." That is the NT teaching on how much.
Jesus himself did not tell his disciples what percentage they should give; rather,
"Give, and it will be given to you. They will pour into your lap a good measure--pressed down, shaken together, and running over. For by your standard of measure it will be measured to you in return."
There is no percentage, only that we will receive back in the same measure that we give. Some will purpose/measure more than others, but this is something every believer must come to terms with before his Lord.
Jesus does refer to tithing in Matthew 23:23, "Woe to you, scribes and Pharisees, hypocrites! For you tithe mint and dill and cummin, and have neglected the weightier provisions of the law: justice and mercy and faithfulness; but these are the things you should have done without neglecting the others."
But who is Jesus talking to? Scribes and Pharisees. These words were not directed to his disciples. He addresses this rebuke to those who were still under the Law of Moses. They were under the whole law, including tithing. We, his disciples, are not. Why would NT believers be expected to keep only part of the law (storehouse tithing), and not all of the law?
Though Jesus was a Jew, born into the teachings of the Law of Moses, He came teaching the Kingdom of God. He commanded his disciples to seek first the kingdom of God (Matthew 6:33).
Kingdom giving is a natural expression growing out of all that is implied in "seeking first the kingdom." We give joyfully and liberally to kingdom causes because that is what Jesus said we are to seek. That doesn't mean part of that giving can't be to our local "storehouse" (of course it can), but it isn't FIRST in what we seek. Kingdom is.
Imagine the Good Samaritan passing by the injured man on his way to Jericho saying to himself, "poor guy, wish I could help, but my tithe has to go to the storehouse..." To me that is a woefully distorted view of all that Christ taught concerning loving God and our neighbor. To think all I have to do is faithfully deposit my entire tithe to First Baptist Church, and somehow that is supposed to cover all those other needs the Lord might want me to do something about. For example, giving towards famine relief efforts of the 14-million people in Africa!
What we teach new disciples in our church planting is not OT storehouse tithing, but NT giving to the Kingdom. The majority of our house churches give upwards of 70% of their monies to kingdom causes. Individual disciples we work with commonly give 30% or more of their earned income to the Kingdom.
The way we approach the subject of tithing/giving/kingdom finances is to start with Matthew 6:33. If we are to seek first the Kingdom, what is implied by that?
We then take a look at all the passages in the NT about how money was gathered, what it was used for, and what things got financed in the early churches.
In a nutshell, what comes out of this investigation is that 1st-century disciples giving went to advance apostolic ministry, helping fellow brothers in time of need (famine relief), and providing for widows/orphans.
We contextualize these findings and basically say:
2) needs of the saints
3) needs of not-yet-believers
To me the issue is not whether or not a believer should give to the Lord's work (of course they should), but WHERE it is deposited, and how it is used. I affirm again, kingdom giving trumps storehouse tithing.