If it's not a tear but just a round hole it's usually fine. Pump up the tire and check for bulging or the tube being visible through the hole. Medium to serious bulging could be trouble down the road but if you just get a tiny bit of tube visible then use a boot of some type. Duct tape should work fine long term but check it every so often. I've had so many nails in thin walled lightweight, high pressure road tires that needed no boot or anything else I've learned not to worry too much with small round holes in the tire and if your tire has a thicker tread/casing and low pressure tire you should have even less to worry about.