Put sugar, margarine and milk into a large, deep, microwaveable bowl. Microwave on high for 4 1/2 minutes. Take out and stir. Place back in microwave for about 5 minutes on high. Remove from microwave, add marshmallows and chocolate chips, and stir until melted. Turn mixutre out into a 9x9 cake pan and refrigerate 1 hour or until set. Cut into pieces. Times may vary according to micorwaves.