Instructions
Deal with the Tank Head first. This part of the Dragon Tank will heal the other sections, negating any damage you inflict. Focus on the Tank Head by having Chrono and Lucca use the Att command until it is destroyed.
Attack the Grinder. This is the tank's wheeled section, which it uses for rolling attacks. Destroy it in the same way you did the Tank Head, using the Att command with both Chrono and Lucca. You can also begin using Chrono's Cyclone attack at this point, which will deal damage to both remaining parts of the Dragon Tank.
Destroy the Dragon Tank body by continuing the Att commands with Chrono and Lucca. Inflict additional damage by using the Dual Tech Fire Whirl. When the battle is finished, you'll receive 40 experience points and 500 gold.