dice.jswidler.com
10,000 throws with small perturbations in the starting conditions should be distributed evenly across all sides of the die.
Alternatively you could use RNG to generate a fair result, simulate the throw, and then set the sides of the die to produce the result from RNG. This is all academic though and I imagine anyone using the site won't be bothered.
I did think about changing the rotation speed of the dice before you throw, kind of speed it up and slow down. I first added the shuffling effect if you hold them; kind of a shell game animation. If I improve it more, occasionally giving some dice a swift spin would make it harder to defeat I think.
Like you say, this is intended for people who are not going to cheat each other and just want to have fun, so I won't make it worse to account for it.
I guess it works better on mobile with a swipe. I could change space to hold it a brief moment and throw it harder. Now that I am looking at it, that is probably what you mean.
I think I want it to use physics in the end though, not map an RNG result at the end. You can see the faces and what you get is like a real die. If someone can beat it, maybe that is good for them.