You should just ask your vet. Vets will take into account the insects in your area, as well as your dog's coat and lifestyle.
Is the med X legal in your country?, dunno, but you can order here your dog drugs. Can I mix X and Y?, dunno, order both and read the contraindications later. Are this meds dangerous for my other pets like my "always-chewing-dog-ears" cat, or my ferret? this web don't give you any clue. I know cases of kitten killed by the wrong treatment; Can you calculate the right doses for your big but starved and weak new rescued pet?... etc, etc...
Of course the owner can and should take some time to educate itself about recognising diseases (and much specially poisonings) of his pet, but good and comprehensive manuals are available in your book store, and of course to identify what kind of roundworm could or not have your dog is not trivial at all for a normal owner.
The guy that that puts all in his tank to cure "don't know what's this thing growing in my fishes" is sadly very common in aquariums. He/she kills currently much more aquarium fishes than the real diseases do.
This is the same problem we have in embedded systems diagnostics. We used to make a list of failure modes, and then a list of diagnostic tests. A given test may detect multiple different failures and I've made grids exactly like this. I always advocate for finding the minimum set of tests to detect all failures (to minimize false positives and simplify software). I was going to make the same point in this case, but parent already did.
To be clear, sometimes it's sufficient to detect failure without knowing exactly what the problem was. For specific diagnostics you may want POST to handle that, but at runtime you may only need to detect that something has failed.
Revolution + Sentinel Spectrum + (Flea4X or K9 Advantix II)