For a product with a single SKU that has both list and sale prices, the sale price always takes priority and the volume price table is rendered when the sale price is specified using volume pricing. To break it down further, there are several scenarios:
The single SKU has volume prices set in both the list and sale price lists. In this case, the volume price table is displayed but it is populated with the prices specified in the sale price list.
The single SKU has a volume price set in the list price list and a non-volume price set in the sale price list. In this case, the volume price table does not appear on the Product Layout; only the non-volume sale price is rendered.
The single SKU has a non-volume price set in the list price list and a volume price set in the sale price list. In this case, the volume price table appears on the Product Layout and contains the sale volume prices.