Question

As the question suggests, I need to round up or down to closest 20, with the exception of numbers from 0-14, all must round to 20, because no zero values are allowed.The table has not to be updated with new values.For now I have managed only rounding up or down to the nearest 100 as seen below:

 CASE WHEN ROUND(number,-2)=0 THEN CAST(ROUND(number,-2)+100 AS DECIMAL(18, 0)) 
      ELSE CAST(ROUND(number,-2) AS DECIMAL(18,0)) END AS [NUMBER]

Answer 1

Try this:

DECLARE @testValue Int = 35;

SELECT
  CASE
    WHEN @testValue BETWEEN 0 AND 14 THEN 20
    ELSE ROUND((@testValue * 1.0) / 20, 0) * 20
  END MyRoundedValue;

There may be a more optimal approach, but this was the first solution that came to mind. The * 1.0 is to force conversion to a floating point number so that the / 20 will produce fractional results. The result is rounded using ROUND then multiplied back by 20 to get your final “rounded” value.

Edited to take your special case of 0-14 into account…