rankx by group

I am using the below formula to rank sales results.  I would like to group the ranking by a column of Profit Center's.  What can I add to the below formula so that the ranking column adds a ranking based on the profit center number?

Rank = RANKX('Sold-To Database','Sold-To Database'[Total Sales],,DESC,Dense)

Profit Center   Total Sales

600005            50,000

600005            15,124

600015            16,399

600116              9,131

600015              7,653