If it is a matter of considering options, another sensible way that A-bombs come up in a combat context rather than strategic war-ending weapon would be to consider using them in China.
By summer 1945, the IJN was a spent force, the IJA on the other hand still held much of China. The die-hard anti-surrender elements would I suppose have been largely Army generals who knew their forces on the continent were still undefeated.
So an alternative war plan to the options of either A-bombing Japan or invading Japan, or doing nothing more than starving out Japan, would be for the Allies to greatly raise the pressure on the Japanese stronghold in China.
That's the context in which I'd think use of nukes "tactically" would come up. Though the point is, to amass sufficient enemy force so that the rare and expensive and tricky to deliver giant bomb gets a whole lot of enemies at once--such a scale of death would I'd think pretty much automatically cross the line from "tactical" to "strategic," though not in the sense that we speak of "strategic bombing" or "strategic nuclear weapons"--these are intended to win wars first of all by inflicting levels of damage such that the enemy is deterred from war as an option, second if they are foolish enough to refuse to be deterred, devastate their ability, not as armies but as a society, to fight the war.
"Tactical" use of even the relatively "small" nukes Los Alamos was first able to make merely means using them in contexts where such deterrance/total devastation is not intended or expected; the scale of damage they do hardly fits the sort of image the word "tactical" normally conjures up!
Someone should point out, in addition, as CalBear mentioned, to there being a limited supply of fissionable materials, the early A-bombs of either design (Gun-Uranium aka "Little Boy"; implosion-Plutonium aka "Fat Man") were very heavy by WWII bomb standards; Americans could only deliver them with the B-29, a specially modified version at that just capable of carrying one bomb, and while some British bombers would have less trouble accommodating the bomb, being lower-altitude and I believe slower than the stratospheric, pressurized Superfortress, these British bombers would be unlikely to survive their own bomb!
What is more, as late as the Operation Crossroads Bikini tests some years after the war, the first "shot" of the planned three tests, "Able," was delivered by the Air Force as an air drop. They missed the intended target by nearly a mile! It very largely invalidated the shot as far as scientific value was concerned. And demonstrated the difficulty of aiming an A-bomb at this stage.
That doesn't matter so much when one has a frankly "strategic" target such as a city, that is sitting immobile in a known location with known defenses.
In a battlefield context, especially one like China, where the enemy probably won't be doing what you hope or want them to, the precise best target may not be known and if known will be shifting. Add to the bomber crew's apparent inability to strike within less than half a mile of their target when that target is known and hitting it has been practiced, uncertain communications betweeen different divisions of the Army (as the Air Force at the time would still have been technically part of the Army) and the uncertainties of the commanders calling for the airstrike--well, if we had hundreds of A-bombs to spare I suppose nuclear whack-a-mole might have been effective against the IJA in China, though probably horribly costly to the Allied armies too.
I have to admit, using them "tactically" to support an invasion makes more sense. There at least it is the Allies choosing the field of battle whereas the enemy is pretty much forced to respond by concentrating forces in predictable locations, or forfeit a beachhead to their foes. If you've got limited numbers of bombs, that's really the only way to plan to use them in an actual combat situation, to somehow force the enemy to make using it worth your while by perforce having to concentrate at the target.
But the horrible aspects of such a battle, with Allied troops hopefully not but possibly themselves blasted by the bomb, then having to advance directly into the just-nuked blast zone, no doubt to have to dig in just beyond it--or in the middle of it!

against more Japanese defenders, all in the service of an invasion expected to be a major bloodbath on both sides--well, it is a good thing the Japanese surrendered before it came to that.