If you don't know the rate of sales tax and have the sales tax amount you can use this simple method for finding sales tax. Taking your numbers:

Sales amount = 714.91

Sales tax amount 55.99

The formula is

X% of Sales amount = sales tax

x/100x714.91 = 55.99

x=55.99x 100/714.91

= 7.83 percent is the answer.

Sales amount = 714.91

Sales tax amount 55.99

The formula is

X% of Sales amount = sales tax

x/100x714.91 = 55.99

x=55.99x 100/714.91

= 7.83 percent is the answer.