If A1 holds the pre-tax price then =A1*7% will compute the sales tax while
=A1*1.7 will compute the price_with_tax-included.
Now all this is mathematically correct but we work in dollars and cents (or
pound and pennies etc.), so we need to do some rounding to the nearest cent
sales tax: =ROUND(A1*7%,2)
price-with-tax =ROUND(A1*1.07,2)
best wishes