Tartness rhymes with:
hartness, hartness, shortness, abruptness, absoluteness, acuteness, alertness, appropriateness, astuteness, bluntness, brightness, compactness, completeness, correctness, cuteness, directness, earnestness, eyewitness, faintness, fastness, fitness, flatness, forthrightness, gauntness, greatness, hartness, inertness, jointness, lateness, lightfastness, lightness, neatness, politeness, quietness, remoteness, rightness, robustness, separateness, shortness, softness, steadfastness, stoutness, sweetness, swiftness, tightness, unpleasantness, vastness, wetness, whiteness, witness, witness'
Tartness sounds like:
tardiness, teradyne's, thirteen's, thorton's, threading, threatening, threatens, thwarting, tiredness, trading, trading's, tradings, traditions, treading, treating, triton's, trotting