QueenPen
I have this deck as well (it's lovely) and I've also been perplexed by the 3 of Pentacles. Here's what the LWB says for the upright card: "There are benefits now, but they are insubstantial and temporary, competent but not expert."
As someone else mentioned, this is not the only character in this deck balancing something on their head. I know the Page of Cups does as well. My interpretation is that the balancing on the head thing is this decks way of conveying the 'competent but not expert' concept.
Jack of all traits, master of none. That's what came to mind.