Nothing could stop you from rolling the die until you get the wanted number, and then only publishing one result.

To be credible, you'd need a RNG that you can't use without everyone else knowing that you did (if not the specific result), which usually means a third party.

Online D&D uses trusted die-roller websites that keep logs of all the rolls made under one's name; you could have a variant where they just publish a hash of the results, rather than the results themselves.