We didn't see Tom advising Michael to take the Fifth, but I'm guessing he did. it would have been in character for Tom (always advising the safe route) and Michael (thinking he was invulnerable).

Tom didn't discourage Michael from talking to Fredo when they had their private tete-a-tete in Vegas when Michael returned from Cuba--Michael asked Tom to contact Fredo. BUT: When Michael learned that Pentangeli was alive, he asked Tom what Fredo knew. Tom replied: "He says he knows nothing--and I believe him." Duh-h-h again, Tom!