Sure you could save couple cents a week by driving with less weight...but then again, you can save yourself $800-1000 on the fuel pump. The most common premature failure of fuel pumps is refilling it on 1/3-1/4 a tank. The pump heats up during its' operation using fuel as its' coolant. So when you let the gas get low in the tank, the pump starts to overheat, causing premature wear of electrical components. You're not saving enough to notice by driving on lighter tank, so it's best you refill it at half tank instead of waiting for it to get lower.
Ps. During winter, try to keep your tank at full. It will prevent formation of extra moisture, which could give you starting problems and such.