Sorry I'm late to the game. Phillip's answer is correct within ServiceNow. If this is a big need, you can take a look at Explore Analytics. It allows you to run live reports (or trended reports) against ServiceNow, but gives you more flexibility -- including putting data labels and chart totals onto the report.
Take a look at this interactive example with data labels, total, a target reference line, and colors aligned to priority. (Try the header controls at the top to change how the report is published).
These reports can be published to ServiceNow dashboards (live), can use ServiceNow's login (so you don't have to log in separately), and you can control the size of the reports down to the pixel. If you're logged in, you can drill through to the records, or drill down to sub-charts.
You can give it a try here.
