Does Temperature Affect Surface Tension?

I took two cups of water, one hot, one cold, and a pile of pennies. The cups were filled to the brim, and I used a pair of tweezers to slip pennies under the water until a drop spilled from each cup. I ran the test twice. I thought that the cold water would have a higher surface tension. The first test, the hot water cup held 26 pennies, the cold held 28. The second time, the cup with hot water held 17 pennies, and the cup with cold water held 15. If there was a greater difference between the temperatures, if the hot water was boiling, and the cold water was almost freezing, there would probably be a difference, but since I let the hot water sit until I could touch it without being burned, and used tap water for the cold, there was no difference.