My town, Highgate, Vermont (05459) doesn't exist in the Careers database of zip codes. No problem, it's a small place. But it doesn't show ANY jobs within a hundred miles, while a town 15 miles away (Grand Isle, 05458) shows 8 jobs.
Some further checking yielded 05450 (Enosburgh Falls, Vermont, which is the largest town in its area) and 05452 (Essex Jct., which is sizable city). 05453, the other Zip for Essex does work though.
Typing in town names works as expected.