Does your Xfce change the volume settings in %5 steps but you want 2%?

Find the pulsaudio plugin location in xconf:

xfconf-query -c xfce4-panel -l -v | grep pulseaudio
/plugins/plugin-8                            pulseaudio

Use that to set the step to 2%:

xfconf-query -c xfce4-panel -p /plugins/plugin-8/volume-step -n -t int -s 2