Tithing was practiced in the OT, but it is nowhere required in the NT. Paul says "Each of you must give as you have made up your mind, not reluctantly or under compulsion, for God loves a cheerful giver" (2 Corinthians 9:7).
Having said that, I believe that tithing does a lot for us. This is what I wrote in a sermon I preached on Sunday (it is up on my site under Sermons Newskins)
"An easy way to free ourselves from the world's rat race of earning and saving and spending is to set aside ten per cent of our after tax income. It is a method which was already used in the Old Testament. This is income tax time and we know exactly what our income adds up to. Tithing it may seem like a large sum. If we have $40,000 to spend after paying our taxes, we say to God "here is $4,000 for you to provide the new wine skins needed to bring justice to our world. How do you want me to invest it?" God turns it back to us and says "you do the investing for me, and do it as carefully you invest your own money." There are many organizations that collect money and most of it never leaves their home office, and we have seen the bottomless pit of corrupt dictators. That means we need to do our home work. You have to decide how much to give to your own congregation, how much for other needs in Canada, and how much for other churches and missions throughout the world.
Mollie and I have tithed for the past fifty years. We never had much income when we were missionaries for eleven years in India. On one occasion for six months when we were in New Jersey on furlough we were so short of money we used to buy three day old bread for our two children. But we still tithed the small income we had, and to our astonishment we never needed any medical treatment.. I haven't met anyone who said they had become poor by tithing. God is no man's debtor.
Most people who begin tithing set up a budget, and soon find their finances
are ordered and they are in much better shape than before. For a start
the government returns forty per cent to you next year as an income tax
refund. But far more important, you will find that tithing begins to free
you from the power of mammon, the god of money (Matthew 5:24). You
quickly become a partner with God as you invest in his concern for justice
throughout the world. And you will find a growing pleasure in following
the good results of the money you invest. There is nothing more exciting
than new wine skins being filled with the new wine of the Holy Spirit."