So You don't have a workbook, but I assume like this, If you have sales for 10 people in 10 rows, Then you can use Right Click on Sum(sales) and Select Percent of Total.
Alternatively, This Formula
Please attach workbook.
Here I have attached screen shot of calculation. Please go through it and let me know if helps you.
Here you can see the calculation in red rectangle.
and then right click on sales in % of Total and select format and click on percentage like below image.
Please mark correct and helpful if it works for you