Aren't both j2002ba2 and BlackHatCoiner right? Yes, a dice roll produces 2.58 bits of entropy, but no, you're not using all of it when writing down dice rolls. If you roll 1, 2, 3 or 4, you treat the dice as if it's a 4-sided dice that produces 2 bits of entropy. And if you roll 5 or 6, you treat the dice as if you flipped a coin. So you end up with 1.66 bits of entropy on average per roll.
All you have to do is roll a dice 99 times. There's no need to do what you are suggesting. It just takes longer that way. You could even be more anal about it and treat 1,2,3 as heads and 4,5,6 as tails but there's no benefit to doing that.