Notice how the first section of the story involves what Benjamin Franklin said were the only two certain things in the world: death and taxes. Franklin was talking about the fact that even the U.S. Constitution would be subject to future change.
Miss Emily's death at the beginning of the story, and the narrators memory of the history of her tax situation in Jefferson might be what Alfred Hitchcock called "macguffins." A macguffin is "an object, event, or character in a film or story that serves to set and keep the plot in motion despite usually lacking intrinsic importance" (source). Neither the funeral nor the tax issue seem to be about are all that important to the tale of murder and insanity that follows.
Still, we should question whether or not they actually are macguffins.
The taxes are can be seen as symbols of death. The initial remission of Miss Emily taxes is a symbol of the death of her father. It's also a symbol of the financial decline the proud man must have experienced, but kept hidden from Emily and the town, until his death. Since the story isn't clear on why Emily only got the house in the will, the taxes could also be a symbol of his continued control over Emily from the grave. If he had money when he died, but left it to some mysterious entity, (the story is unclear on this point), he would have denied Emily her independence.
Over 30 years after the initial remission of Miss Emily's taxes when the "newer generation" tries to revoke the ancient deal they inherited, taxes are still a symbol of death, though this time, they symbolize the death of Homer Barron.
As we argue in "What's Up With the Ending?", the town is probably already aware that she has a rotting corpse upstairs. Maybe the taxes were just an excuse to definitively see what was going on at the house. The next phase of their plan might well have been foreclosure. They could have used the tax situation to remove Emily from the neighborhood, and to condemn her house. Perhaps they wanted to remove the "eyesore," and to cover up everything Miss Emily says about the past and present of the South.
The fact that they didn't do this might just turn the taxes into a symbol of compassion. Wasn't it out of compassion that her taxes were initially remitted? That the "newer generation" decides to continue the tradition also shows that some of the older ways might well have merit.