In an experiment involving prices for an ice cream scoop, people perceived $7.66 as representing a larger discount from the original $10 price than it actually was (estimating, on average, that it represented a 28.7% reduction, when in reality the difference was 23.4%), and they perceived a price of $7.22 as a smaller discount than it really was, say Keith S. Coulter of Clark University and Robin A. Coulter of the University of Connecticut.
People unconsciously associate certain letter sounds, such as the “s” and “i” in “sixty-six,” with smallness and the “t” and “oo” of “twenty-two” with largeness, and these associations interfere with the accuracy of their quantitative perceptions.
Source: Small Sounds, Big Deals: Phonetic Symbolism Effects in Pricing