Render unto Caesar the things which are caesar's and then render unto the Lord the things which are the Lord's. He gave the command in that order on purpose. You don't tithe the things which are caesar's. They were his to begin with just as the 10 percent on your net was the Lord's to begin with.
Matthew 22:21 They say unto him, Caesar's. Then saith he unto them, Render therefore unto Caesar the things which are Caesar's; and unto God the things that are God's.