Price-slashing failed to rescue a bleak holiday season for beleaguered retailers, as sales plunged across most categories on shrinking consumer spending, according to new data released Thursday.

Despite a flurry of last-minute shoppers lured by the deep discounts, total retail sales, excluding automobiles, fell over the year-earlier period by 5.5% in November and 8% in December through Christmas Eve, according to MasterCard Inc.'s SpendingPulse unit.

When...