Then you're not "tithing", rather you are giving "offerings". Since "tithe" means a tenth...you can't say, "I don't tithe 10%." :confused:
Jesus said that yes you should tithe in Matthew 23:23, but to not forget to show mercy and love while you're at it. Also, the book of Hebrews 7 talks about tithing...Abraham was the first to tithe to Melchizedek. Notice that this action took place *before* the law was given. And Jesus is our High Priest after the order of Melchizedek. So even though, NT Christians are not under OT law, the act of tithing is outside the law all together.
I see it more as a standard to allow God access into my treasure (where your treasure is, there your heart is also). The tithe is a minimum, everything else is considered an offering. It's a percentage set by God through Abraham, when His promises were just being realized by mankind.
And look at the blessing of Abraham fulfilled! In Malachi, God says TRY ME in this and let me prove that I'll open the windows of Heaven and pour out a blessing that you can not contain!:)