Hello, @alanrew,
Starting with the 7.3.1 version of N++, you can change the default word characters list ( any character matched by the regex \w )
Select the menu option Settings > Preferences… > Delimiter > Word character List
Click on the choice : Add your character as part of word
Type in the $ character, in the field
Close the Preferences dialog
Et voilà !
Remarks :
Strangely, the regex \w, still, does NOT match the $ symbol !?. Therefore, a PHP variable name should be matched with the regex \$\w+
A double-click on words , containing the $ symbol or ending with it will, also, select them !
Best Regards
guy038