Nip and tuck has 6 different meanings across 3 categories:
plastic surgery to remove wrinkles and other signs of aging from your face; an incision is made near the hair line and skin is pulled back and excess tissue is excised
"some actresses have more than one face lift"
Minor cosmetic surgery that tightens loose skin.
inconclusive as to outcome; close or just even in a race or comparison or competition
"as they approached the finish line they were neck and neck"
"the election was a nip and tuck affair"
So evenly matched that the advantage shifts from one to the other, and the outcome is uncertain.
even or close in a race or competition or comparison
"the horses ran neck and neck"
"he won nip and tuck"
With the advantage changing hands, or shifting back and forth among the available alternatives.