I’ve never seen an option that does this neither. There is a way! This involves changing what the keyboard shortcuts do.
In the Keyboard Shortcuts options, disable the shortcuts for “Volume up” and “Volume down” by clicking on them and hitting Backspace.
At the bottom, create two new custom shortcuts with these commands:
-
Decrease Volume
amixer -D pulse sset Master 5%-
-
Increase Volume
amixer -D pulse sset Master 5%+
You can change 5%
to a different number if you like.
Now bind the new commands to your multimedia keys.