The whole point of toughened glass is that it is hard to break and therefore hard for the amateur to cut. You need to take it to a glazing company and see if they will cut it for you.
You cannot cut toughened glass as Ian munt says , this is due to it being shaped and cut to size then blasted with a flame to temper it , if you score it or attempt to "break" it along the score it will shatter , you can however cut float and laminated glass to whatever shape or size you want to, is it kitemarked toughened ?? you can tell by the weight and noise it makes when tapped ...(not on the edge of it though )