7.16Melody can tell you what kind of cadence is possible

If the final melody note is C in C major:

good candidate for tonic.

If the melody ends on B:

that might suggest unresolved tension.

If it ends on G:

it could still be over C, because G is the fifth of C.

So melody ending on 5 can still feel complete harmonically.

Do not assume melody must end on tonic to resolve.