I don't think there's anything special you can do if you're routinely adding items with automatic tags from sources that use different wordings for what, to you, should be the same tag. But as with most metadata problems, they are best fixed (manually) when the item is first added to Zotero, rather than letting problems accumulate. There are plugins like Linter for automatic metadata cleanup when adding items, but it doesn't cover your tag issue.

For your existing library that has this problem, you can merge misnamed tags under the same name. It has to be done manually, but it is not particularly difficult.

You would first need to decide which naming you want to make the standard for a given tag. Establishing those personal 'rules' would also allow you to fix incoming tags as above. I am a heavy user of (manual) tags, and I have always tried to establish my tag list for any knowledge area as early as possible, ideally before I start adding items (adding a new tag to many existing items is difficult).

To merge existing redundant tags, in the Tag Selector pane you simply select and rename each tag you want to replace, giving it the standardized name you want it to have. Zotero will merge each renamed tag with any existing one that already has the name you want.