If you want it to display on the product page, you'll need to code the pricing rules into your site theme & also either use a Shopify Automatic Discount or program a script in your shopping cart to apply the same rules.
You could also find an app. e.g. Quantity Price Breaks sounds like it might do what you want?
For example, do you mean you might sell a product for $10 but if the customer wants to order more than 5 of these the cost should be reduced to $9?
I feel like this should be a basic feature in Shopify but the only thing I can see is people adding their own code, adding apps, or using wholesale prices lists which require Shopify Plus:
Anyone have thoughts on this?