sales tax total amount from one cell amount to another cell

[Guest]

I WANT TO GET THE FORMULA IF THERE IS ONE ON HOW TO GET THE TOTAL SALES TAX
ON MY HOME MADE INVOICES FROM AN AMOUNT ON ONE OF THE CELLS TO ANOTHER CELL.

 

[Don Guillett]

First, typing in all CAPS is considered shouting and rude unless one word
for emphasis.
where a2:a22 is the item list and sales tax is in cell a1
=sum(a2:a22)*a1