They are shuffled only once at the beginning of the game and handed over a bit more often than wonder cards.
But they are beautiful and some visible change on the back would be much more of an issue than with wonder cards, as they are face down on their decks and then put face down to the pantheon.
"Dwarf King" French Tarot Card Sleeves - Magnum (61x112mm) (mayday) fit perfectly well ... I would use them.
Standard or Premium Sleeves?