Psychologically dishonest perhaps, which is why it’s so widely used. We seem to give the first part of the number more weight. Same with birthdays. 28 to 29 isn

Psychologically dishonest perhaps, which is why it’s so widely used. We seem to give the first part of the number more weight. Same with birthdays. 28 to 29 isn’t a big deal, but 29 turning 30 is a big deal (or any multiple of ten).