It should be sufficient, those are the same temps I root in and I have no problems. My house average temp is 65 also during this time of year.
The thing is, the higher your temperature gets, the faster mold and rot can multiply. If you go above 80 degrees, mold and rot are more likely to overtake your plants.
Be sure to put something in the bottom of your bin to keep your pots/cups off the floor of the bin, especially if you choose to use bottom heat. I would keep the cuttings in a sunny room, but away from direct sunlight.
If you want to track the temperature and humidity inside your bins for a few bucks, I recommend this combo kit from PetCo, designed for sticking inside reptile cages: http://www.petco.com/product/8193/PETCO-Thermometer-Humidity-Gauge-Combo-Pack.aspx?CoreCat=OnSiteSearch
(They come with tape on them already, be sure to clean the surface with rubbing alcohol and allow to air dry before sticking the gauges, and let them stick for a couple of days before adding humidity).
I used those gauges for my first year of rooting figs. I found that my humidity stayed around 55%-70% and my temperatures inside the bin would be 1 or 2 degrees higher than the room, usually around 67º. By adding a heating pad for backs on an intermittent timer turning on/off every 30 minutes, I was able to get the temperature up closer to 70º, but for the household power I wasted, I didn't notice enough difference in growing to make a difference, so I quickly ditched using bottom heat.