You should control your volume either my mouse scroll as you suggested or by left/right arrow keys.
If arrow keys aren't working, then it's probably a bug described at indicator-sound keyboard controls with left/right ARROW keys broken.
This bug was fixed in the package ido - 13.10.0+14.04.20140213-0ubuntu1.
If the volume adjust is too coarse-grained, try upgrading indicator-sound package (>= 0.5.6) or try to Decrease mouse sensitivity below the standard limit.
Alternatively you can define your own keyboard shortcuts in System->Preferences->Keyboard Shortcuts. As a side note you must have the correct sound mixer device selected in System->Preferences->Sound for it to work properly. This may be a problem source if your volume will not adjust.