If you know the sales tax percentage, you can work out the subtotal and sales tax amount from the total. There's surely an actual formula for this somewhere, but this works.

Say the sales tax is 9.3 percent. You divide your grand total by 1.093 to get the sub total. ( .093 is 9.3% expressed as decimal number)

Example: $7.10 is the grand total. Tax is 9.3%.

$7.10 / 1.093 = $6.4958828 ($ 6.50)

This is your sub-total. To find the sales tax amount, simply subtract your sub from the grand.

$7.10 - $6.50 = $0.6041172 ( $0.61)

This is your sales tax amount.

Say the sales tax is 9.3 percent. You divide your grand total by 1.093 to get the sub total. ( .093 is 9.3% expressed as decimal number)

Example: $7.10 is the grand total. Tax is 9.3%.

$7.10 / 1.093 = $6.4958828 ($ 6.50)

This is your sub-total. To find the sales tax amount, simply subtract your sub from the grand.

$7.10 - $6.50 = $0.6041172 ( $0.61)

This is your sales tax amount.