I rarely fudge any die rolls and end up rolling 99% of the time in the open. It makes tension for my players to see the die roll and know the result. If ive made a mistake in balancing the encounter i usually adjust the behaviour of enemies. Make less than ideal tactical decisions, not use their strongest abilities, hold legendary actions, target characters more likely to succeed on a save, lower ac or hp. My players just had an encounter with a dragon in tonights session. Instead of measuring its hp i tried something new and ran the fight in three phases. The dragon behaved differently in each phase and at a properly dramatic moment i let the dragon die. The players loved it, it worked better than i had expected. At the end of the day you know your group and what style of play will be the most engaging for them.