How much money do you save on oil by keeping your thermostat at home at a lower temperature?

My parents insist on keeping our house about 65 degrees in the winter in order to save on oil, which in turn saves money. About how much more would it cost to heat the house say 5 more degrees?|||1 degree in my house costs $40-$60 a month|||5 degrees sounds like you live in an older home so anywhere from 100-300 a month