The cost basis that I calculated from an RSU stock sale does not match the cost basis on the 1099-B. Which cost basis should I use?

I followed the "guide me step by step" process to determine the cost basis for three separate RSU sales and none of the three calculated cost basis matched Box 1E on the brokerage statement.  One was reasonably close but the other two calculations were much lower than the cost basis on the 1099-B form.  Which should I use?