Blood pressure will slightly alter all the time, there are many factors to take into account. Even if you are still digesting food, the pressure will alter because more blood is required to be transferred to the gut. To be honest, it would be more worrying if your pressure was exactly the same each time you measure it. You have very good blood pressure by the way.
Ed is correct, BP is dynamic and is affected by many things. As long as your readings are under 120/80 you're doing great.