When creating a 100% Stacked Column chart, there is no option to alter the display units for the chart. However, the charts retains whatever display unit setting was selected when using a different visual.
Steps to reproduce:
Create 100% Stacked Column chart from any data.
Open Format tab of visualisations pane.
Expand Data lables and see that there is no "Display Units" option.
Change the chart type, check the format tab, and alter the "Display Units".
Change chart back to 100% Stacked Column and see that it remembers the selected "Display Units" option.