Go To:  WooCommerce–>Dynamic Pricing–>Category Tab

When you want to put an entire category on sale use the Dynamic Pricing Tool.

You can set up a percentage-off or dollar-off sale for each category, except Non Discountable products.  Even if Non Discountable products are in the category you select, such as Books, those specific products will not be discounted.

For each category, toggle the Enabled slider to enable a category sale.

Choose the type of sale you wish to run:  price discount or percentage discount.

Then enter the amount:  a dollar amount (no currency sign needed) or a percentage (no percentage sign needed)

SAVE your changes and your are done!