Taxation is a technology that is unique to the Royal Naboo, and can be researched at the Fortress in Tech Level 4. It costs 225 Food and 400 Nova, and reduces the cost of all military units by 10%.
This technology will allow the player to field a larger army for the same price, giving a small advantage. It should be researched as early as possible to gain maximum benefit from it.
This is one of two unique upgrades that benefit a Cannon. The other is Battle Armor, also a Royal Naboo technology.
"The Royal Naboo may develop a unique taxation system by means of this Tech Level 4 technology, which translates into a greatly reduced production cost for all its military forces."
—Manual description