Jim is freed from slavery at the end of the novel. The Duke and the King are tarred and feathered and ridden out of town. Huck is also given the news that he can return home, if he wants to, because his father is dead.
In various ways, these are the instances of justice being served in the final chapters of the novel.
The example of Jim's freedom is the only purely positive outcome of these three, however, as the other examples include death and punishment that offer new emotional conflicts for Huck.
Though Huck is not strongly affected by news of his father's death, he is not overjoyed by the news either and he is saddened to see the two rogues, the King and Duke, brutally punished by the townspeople.
The freedom that Huck has achieved in the end has been earned though moral and physical work and so may also stand as example of justice being served.