A question about how much to tithe?

I know 10% is the biblical amount for tithing. However, what if over the past year I have only given maybe 5%? I have the money now and feel called to "give what I couldn't." So what's the question? Do I have to tithe my 10% to the church? Can I give that percentage to another organization or person in need? Also, is it biblically correct to tithe 10% of a monetary gift?