It's no secret that Fives was one of the first victims of the growing Galactic Empire and although people have long suspected foul play in his death, CT-5555 never truly got the justice he deserved. However, it looks like Star Wars: The Clone Wars Season 7 finally gave Fives some form of justice after all this time.
In the sixth season of The Clone Wars, Fives looked into Tup's case when CT-5385 suddenly killed the Jedi Master General Tiplar. In his investigation, Fives realized that the inhibitor chips implanted into the Clone Troopers had a dangerous purpose and tried to warn Rex. Sadly, this led to Fives being accused of planning Palpatine's assassination, and Commander Fox later killed him before he could fully reveal everything to Rex.
Interestingly, Fives was not able to save himself but he somehow managed to save Rex and Ahsoka Tano. In The Clone Wars Season 7 Episode 11, Rex ordered Ahsoka to "find Fives" right after Darth Sidious executed Order 66. This led to Ahsoka looking into Fives' files and realizing that the inhibitor chips were the key to the Clone Troopers' murderous behavior.
It's not the justice we were hoping for Fives but it's the closest thing we can get on the series. It's satisfying to know that although Fives couldn't do anything for Tup or himself, he would later be the one to help Rex and Ahsoka.
Star Wars: The Clone Wars Season 7 Episode 11 is currently streaming on Disney+.