Glass is toughened by cooling the outside faster then the inside, which due to the way glass is formed causes there to be stored stress in the glass. When breaking the glass this stored stress has to be over come before you break the glass, giving it extra 'toughness'. (Glass can also be 'over toughened' where the stored stress is to high, and can the be cause to shatter by little things like change in temperature, but that is irrelevant to your question).
To answer your question It might be enough, but it depends on how much it has been toughened, and how much redundancy you want in the strength of the glass.
Also sort of unrelated toughened glass shatters differently to untoughened, as it will hatter into small pieces instead of the cracks you see when untoughened glass breaks.