ExploderWizard
Hero
Fudging without telling the players about it every time - or even while denying it - is no more lying or dishonest than not showing other players your hand when playing cards, or bluffing when playing poker. D&D - at least, most editions of it, including 5e - does not assume that the DM tells the player everything that's going on behind the screen.
There is no need to mention every instance of fudging or even when it might happen as long as the players know at the beginning that these are possibilities. This is quite a different thing than telling the players everything that is happening behind the screen. There are many things the players won't know or have to discover through play, and IMHO one of those things shouldn't be whether or not the DM may be fudging die rolls and disregarding the results of fair game play in favor of pushing results toward a pre-defined outcome.
It is enough to mention some things may be changed ad-hoc to increase the fun of the game at the start of the campaign and if the players are all cool with that, never having to mention when or if you fudged anything specifically.
There can be plenty of deception going on behind the screen without impacting fair outcomes. Sometimes I will roll a die for no reason whatsoever even though I know there won't be a chance of a random encounter. The players don't know that a particular area is safe from random encounters so the occasional roll keeps them guessing.
As far as the cards analogy it doesn't work because the DM isn't an opponent of the players. An NPC might certainly lie or try and bluff, and PCs interacting with what they don't know is an illusion isn't really lying either. There may lots going on behind the screen but a game the players wouldn't willingly want to participate in need not be one of them.