All bills intended to raise revenue for the United States of America, including tax bills, must start in the House of Representatives. This law is set forth in the U.S. Constitution. The same section of the Constitution also gives Congress the authority to collect taxes in the first place.
The President of the United States can, and often does, suggest changes to the country's current tax laws, but he does not have the power to enact those changes himself. The proposed changes must be given to the U.S. Congress, which must vote on them before signing them into U.S. law.