For every 100 bells you spend at Tom Nook's, you earn one point.

Bad bro 'stache - 2,500 points
Banana - 500 points
Hero's cap, Majora's Mask, or Samus mask - 6,000 points
Hero's clothes, Varia suit, or Wario hat - 5,000 points
Kart - 10,000 points
Midna's mask - 6,500 points
Peach's parasol - 4,000 points
Toad hat - 3,000 points
Triple Shells - 800 points
Yoshi's egg - 1,000 points