Pour the cranberry juice into the blender, reserving 1 tablespoon.
Place three tablespoons of sugar on a small plate, and pour the tablespoon of cranberry juice on another small plate.
Dip the rims of 4 glass in the cranberry juice, and then in the sugar.
Place the remaining ingredients in the blender, keeping a few berries back for garnish.
Blend for 30 seconds, or until smooth.
Pour into a pitcher through a fine mesh strainer to catch the cranberry pulp. Mash mixture wth a spatula to help it through the strainer faster.
Pour the strained margarita into glasses and garnish with reserved berries on decorative toothpicks.