I'm using tags, but the audio effect still plays. I'm wondering if I need to include an event connected to clicking the Left mouse button as that's what triggers the sound but I'm not sure how to do this.
In some way, whether it's through the variable Mario suggested or through a mouse click, you'll need some event that turns it off. And once you do, make sure there's nothing else that will trigger it starting again. The Audio.Stop All should stop all sounds from playing regardless of the tag.
Here's an example of how I'm using a mouse click on a sprite event to start music playing. Stopping it is done the same way.
+ Mouse: On Left button Clicked on NewGameButton
+ System: [X] Is ChoiceMade
-> Functions: Call PlayEffect (Name: "UI_Quirky30")
You'll notice that calls a function. One of the things I do to help keep things organized is to create an entire event sheet just to handle audio events and include it in any other event sheet that needs to play audio. That way I just call a function to play music or sound and pass the file name. If I need to adjust things or change the way all audio is played, I can change the function without having to find every single event where I play audio.