If you put a candidate you really like through a panel, and it comes back with 50% positive, 50% negative, you have no choice but to have other people talk to her.
There is always a choice. You can not hire that person. In fact, I'd say that's the "no choice" decision. If half your team doesn't like the candidate, having more rounds of interviews isn't going to change that. You don't hire that person (unless you as boss make the decision to overrule that half of your team, and you don't need more interviews for that).
What you (as a hiring manager) absolutely does not want is for some of your key talent to feel dissed and start looking for jobs for themselves... something that is a real risk in these days where the market is super-favorable to good engineers.
And the best way to lose good talent is by wasting their time. And needless rounds of interviews are a waste of time. Seriously, as other have said, 3 rounds: prelim HR screen, manager qualifications check, & team fit (either as a group or a serious of 1-on-1s). Maybe a 4th if you need a tie-breaker between 2 candidates.
More than that is a red flag of management buried in bureaucracy.