Round the regular price to the nearest whole number. $19.99 would round to $20.00.
Multiply the 1st number of the price X the 1st number in the percentage off.
2(the first number in the price of $20) times 1(the first number in the percentage off) = $2.00. That is how much you will save.
If the item price rounds to $50.00 and the store offers 40% off - 5 X 4= 20 .
$50 - $20 = $30.
I summary... The first number of the regular price (rounded) multiplied by the first number in the percentage off equals the amount you will be saving. Subtract that amount from the regular price to figure the aproximate sale price.