The problem with tithing is that it only represents a portion of us. You will find no New Testament injunctions that require it. What you will find is an infinitely wealthy God who has impoverished himself in order to make us rich. You will see the total unreserved self-donation of the God-man on the cross. The cross is a flag firmly planted in the ground of history that communicates the story of a generous God. If the cross communicates anything it communicates that the God is anything but stingy. He gives all. He gives himself.
When Paul wants to talk to a congregation about giving he does not take them back to Old Testament tithes and offerings. He takes them down the Via Dolorosa. He takes them to the place of the skull. He reminds them of the bounty of God toward them in the gospel. He then helps them understand the link between believing the gospel of God and living a life of generosity.
They receive Christ as gift and then in gospel freedom follow him as example. If we would follow Christ he would have all of us not just a portion. We are called to take up a cross and follow Christ. Our generosity is to be cross-shaped. The cross does not require 10 but 100 percent. Our whole life and our death are required of us if we would show the generosity that is demanded in and reflective of the gospel.