The idiom ten a penny means very common or ordinary, and the entailment follows that by saying that chemists are a dime a dozen, which is another way of saying that they are very common.
Context: No disrespect intended, of course, but you chemists are a dime a dozen.
Hypothesis: No offense meant, of course, but you chemists are ten a penny.

Is the hypothesis incorrect? (Yes, no, or unknown)?