Sharp XE A407 Tax/discount issues. Programming?

Help!
When checking out customer with no sale items....everything is all good. However, if I apply a discount by hitting subtotal, then apply discount, it still charges the tax based on prior amount, which in turn charges the customer double tax. Can't figure it out.

Also, is there a way to apply a discount to individual items instead of to the whole sale at the end? Have tried and tried to understand Manual and just don't understand.
thank you in advance for any assistance!