Why buy a bottle of sherry unless you know it is going to be drunk and enjoyed? The days of "having to" have something to offer (a la Hyacinth) are happily gone. So many people are driving, it is unfair to assume they will want alcohol, and if we are talking about a drink before dinner, many people will start with the wine they plan to go on drinking throughout the meal.
If on the other hand, you enjoy an occasional noggin of sherry, keep it until it is finished and then buy another bottle next week 
I keep fino in the fridge and amontillado or pale cream at room temperature, but never for too long, I wonder why? 