Prohibition on United Nations Taxation Act of 2005 - Prohibits the United States from paying any voluntary or assessed contribution to the United Nations (UN) or any of its agencies (including the United Nations Development Program) if the UN attempts to impose or advocates the imposition of any tax or fee on any U.S. person, or attempts to borrow funds from the International Bank for Reconstruction and Development (World Bank), the International Monetary Fund (IMF), or any other similar or regional international financial institution.