First, there is no explicit New Testament command to tithe. Impossible, right? Look it up. If you can find one I have overlooked, I am open to correction. Tithing is a good idea and a commendable practice, but not a command. Jesus didn't say don't do it. He did say it's not necessarily the most important aspect of our giving (Matthew 23:23).This is true and one of those things I rarely hear mentioned in most churches. After the return from exile, the Jews moved from the tithe system to the temple tax system. Every Jewish male was expected to pay a half-shekel per year. Jesus's attack on the moneychangers in the temple was for practices surrounding the payment of this temple tax. I'm willing to bet that the current Jewish practice of maintaining synagogue memberships is descended from this practice.
The actual New Testament practice on giving was to give what you could afford. For instance Acts 4:32-37 where Barnabas donates the profit from selling property to the church.