If you only want to cycle through enemies that you've engaged, change your "While weapon is drawn" targeting filters to only "aggroing enemies".
/characterconfig
Control Settings
Filters
Enable target cycling: While weapon is drawn.
These filters affect the movement of the cursor using the "Move Cursor/Target Cursor Left" and "Move Cursor/Target Cursor Right" keys (/keybind, System), not the tab targeting, so that you will target only aggroing enemies when your weapon is drawn. You may set one of these to Tab if you wish; just be aware of your filter settings and make sure you can target whatever you intend to target in both stances.
This is a soft target by default and requires pressing the Confirm keybind to convert to a hard target. If you want to make it a hard target always, /characterconfig, Control Settings, Target, Switch target circle to target select.
