Taxes, discounts, tips and more

(Original price) + [(Original price) $\times$ (tax/tip in percent)] = (New price)

(Original price) $\times$ [1+ (tax/tip percent in decimal)] = (New price)

(Original price) - [(Original price) $\times$ (discount in percent)] = (New price)

(Original price) $\times$ (1 - discount percent in decimal) = (New price)