A pendulum works based on body intuition. It doesn'g fo anything by itself; it expresses the unconscious intuitive/psychic perception of the person who is using it.
Selecting Tarot is seemingly based on randomness and synchronicity. There is truth to that, to be sure. However, the shuffling and/or drawing is done according to the intuition of a human being. Thus it is not entirely different from using a pendulum. The methods of individual Tarot readers vary; personally I like to let my hand hover over the cards until I feel something like a tingling in my middle finger. Under certain circumstances (like lack of space for fanning out the deck), I simply shuffle and cut it, then take the required number of cards from the bottom.
When using a pendulum, I often write the various options on cards that I then turn face down and mix up as not to let my conscious mind potentially influence the result. Experience showed me that it's almost always the card on the bottom that the pendulum agrees to! (But that's just me.)
Of course, I could also use a pendulum to select Tarot cards, even though it's not necessary; my left middle finger serves me well.
