Try something like this
DECLARE @Income INT = 700000;
DECLARE @TaxPercentage INT = 0;
IF(@Income < = 250000)
SET @TaxPercentage = 0;
ELSE IF(@Income > 250000 AND @Income <= 500000)
SET @TaxPercentage = 5;
ELSE IF(@Income > 500000 AND @Income <= 1000000)
SET @TaxPercentage = 20;
ELSE IF( @Income > 1000000)
SET @TaxPercentage = 30;
SELECT @Income, @TaxPercentage