The tithe is specifically mentioned in the Book of Leviticus, the Book of Numbers and also in the Book of Deuteronomy. The tithing system was organized in a 7 year cycle, corresponding to the Shemittah cycle. Every year, Bikkurim, Terumah, Ma’aser Rishon and Terumat Ma’aser were separated from the grain, wine and oil (as regards other fruit and produce, the Biblical requirement to tithe is a source of debate). Deuteronomy 14:22 Unlike other offerings which were restricted to consumption within the tabernacle, the yearly tithe to the Levites could be consumed anywhere (Numbers 18:31). On years one, two, four and five of the Shemittah cycle, God commanded the Children of Israel to take a second tithe that was to be brought to the city of Jerusalem. Deuteronomy 14:23 The owner of the produce was to separate and bring 1/10 of his finished produce to Jerusalem after separating Terumah and the first tithe, but if the family lived too far from Jerusalem, the tithe could be redeemed upon coins. Deuteronomy 14:23Then, the Bible required the owner of the redeemed coins to spend the tithe “to buy whatever you like: cattle, sheep, wine or other fermented drink, or anything you wish.” Deuteronomy 14:22–27 Implicit in the commandment was an obligation to spend the coins on items meant for human consumption. According to the Hebrew Scriptures, the second tithe could be brought to Jerusalem any time of the year and there was no specific obligation to bring the second tithe to Jerusalem for the Festival of Sukkot. The only time restriction was a commandment to remove all the tithes from one’s house in the end of the third year. Deuteronomy 14:28
The third year was called “the year of tithing” Deuteronomy 26:12–14 in which the Israelites set aside 10% of the increase of the land, they were to give this tithe to the Levites, strangers, orphans, and widows. These tithes were in reality more like taxes for the people of Israel and were mandatory, not optional giving. This tithe was distributed locally “within thy gates” Deuteronomy 14:28 to support the Levites and assist the poor.
http://en.wikipedia.org/wiki/Tithe