In a large bowl, cream together the margarine, peanut butter, 1/2 cup white sugar and brown sugar until smooth. Beat in the egg. Combine the flour, baking powder, baking soda and salt; stir into the peanut butter mixture. Cover and chill dough until firm, about 30 minutes.
Preheat the oven to 375 degrees F (190 degrees C). Roll chilled dough into 1 inch balls. Press a caramel candy into the center of each ball so that it is completely covered with dough. Roll balls in remaining sugar and place 2 inches apart onto ungreased cookie sheets.
Bake for 10 to 12 minutes in the preheated oven, until set. Cool on baking sheets for 2 minutes before removing to wire racks to cool completely.