How can I view the sale price in POS for an item?

Cursor up to the item and press F2. This will display a box with all pricing and quantity information.

Note: The total discount for the invoice is shown at the top of the screen.

If you have SWAT Search installed (Bicycle Bundle, RMS Toolkit, Matrix Master or standalone), the active sale price is shown in the right-hand column. Mouseover will list details (start/stop dates or discount schedule).