I don't see a question, but I assume you're wondering why it doesn't work.
Try this instead:
tell application "System Events"
try
set _groups to groups of UI element 1 of scroll area 1 of group 1 of window "Notification Center" of application process "NotificationCenter"
repeat with _group in _groups
set _actions to actions of _group
repeat with _action in _actions
if description of _action is in {"Close", "Clear All"} then
perform _action
end if
end repeat
end repeat
end try
end tell
Thank you, your suggestion is a good way to repeat over a list. The original solution works but checks for "Clear All" first before moving on to check for "Close". With the list you suggested, for some reason a group of alerts that is expanded, this will close all but the last alert. ¯_(ツ)_/¯
Yours does work better! The reason it didn't work for me was the end tel typo, which I missed at first. Once that was fixed, it works great and, as you mentioned, doesn't leave one notification at the end. 
Ahh... I missed that too. Must have hit the delete key right before I shared this. I updated the macro and the jpeg to show the missing "L".
For anyone who doesn't know what is going on (because its since been updated), the original macro was missing 1 "L" in the last "tell" of the script, so it was actually "tel" ... which will break.
Thanks for the good catch @noisneil
Thanks for that macro. Clearing notifications was going to be my next project. Now I'll have to think of something else to do.
Emyr
My pleasure. I'm sure this macro can be tweak to perform better. I'd love to see your updates if you work on it.