Rotate@BarChart[RandomReal[1, {4, 5}], ChartLayout -> "Percentile"]
Even though the FullForm generated by BarChart is Graphics expression, Rotate has no effect on BarChart and many other packaged plot functions. However, it's frequently necessary to rotate, scale and align such plots to other graphics in composite data visualizations (eg, imagine a heatmap augmented with row and column descriptive statistics visualized with two corresponding BoxWhiskerChart)
How can rotatable, translatable, etc. graphics be extracted from functions like BarChart and BoxWhiskerChart?