Proverbs 3:9 gives clear direction for tithing on gross income (before taxes) vs. tithing on the net (after taxes): “Honor the LORD with your wealth and with the best part of everything you produce.” Tithes should be given from the first fruits—your income before any expenses or other obligations are taken out—the gross, not the net. (Also read Deuteronomy 26.)
Brother Copeland tithes off the gross and considers the money that goes for taxes as a seed into the government. Since he started doing this, he has never failed to have more than enough to pay his taxes when they are due.