Junk Sweep

Junk Sweep (also known as Cleanup in Kingdom Hearts II Final Mix) is a mini-game in Twilight Town that both Sora and Roxas can play although only the latter receives munny for it. To play, look at the help wanted sign in the Market Street: Tram Common.

The objective of the game is to swing your weapon at the various piles to knock them away. The less points Roxas has, the more munny he will receive. While playing as Sora, it is required to complete in a certain amount of time to complete the journal.

Sora's reward
To unlock the secret ending in Standard Mode (and Proud Mode on Kingdom Hearts Final Mix), you need to complete Jiminy's Journal. Part of finishing Twilight Town's journal entry involves playing this mini-game. The Jiminy Objective is to complete with less than 6 points.

Strategy
Swing at the various junk piles to knock them away. At the end of each combo, the piles you hit go flying and explode. Any piles that they hit are blown up, too. Use this to your advantage and aim various piles at other piles. A good strategy is to finish a combo with another pile nearby. This way, both piles go flying and have a chance of crashing into even more.

Advanced tactics
There are two tricks to scoring as few hits as possible. Begin by equipping any ability and/or weapon you have with a Negative Combo, such as the Fenrir Keyblade. Use the fact that you can push around the piles of junk to your advantage. Try placing them in corners and at set distances from where a combo begins to increase other that you can hit.

Another trick is to unequip all of your abilities, except the Negative Combo ability. Again, equip the Fenrir Keyblade. Push the piles of trash into one big pile, and once you attack, Sora will perform a finisher, and not a combo. This should get rid of the trash in under six swings, which is the objective in Jiminy's Journal.