Refer the below sample test quesry for your reference and implement it as per your code logic at insert time.
SQL
Declare @SingleBedPer INT 
Declare @DoubleBedPer INT 
Declare @SingleTotal decimal(18,2)  
Declare @DoubleTotal decimal(18,2)  
DECLARE @TaxFreeAmount 	decimal(18,2) = 0
DECLARE @SlabOneAmount 	decimal(18,2) = 0
DECLARE @SlabOneTax decimal(18,2)= 0
DECLARE @SlabTwoAmount 	decimal(18,2)= 0
DECLARE @SlabTwoTax decimal(18,2)= 0
DECLARE @SlabThreeAmount decimal(18,2)= 0
DECLARE @SlabThreeTax decimal(18,2)= 0
 
SET @SingleBedPer = 12 -- get your single bed percentage based on your condition for record
SET @DoubleBedPer = 12 -- get your double bed percentage based on your condition for record
SET @SingleTotal = 100 -- get your single bed Amount  based on your condition for record
SET @DoubleTotal = 200 -- get your double bed Amount  based on your condition for record
DECLARE @SingleBedPercentAmount decimal(18,2)= (SELECT CONVERT(DECimal(18,2),@SingleTotal) * (CONVERT(DECimal(18,2),@SingleBedPer)/100))
DECLARE @DoubleBedPercentAmount decimal(18,2) = (SELECT CONVERT(DECimal(18,2),@DoubleTotal) * (CONVERT(DECimal(18,2),@DoubleBedPer)/100))
if(@SingleBedPer = 0 and @DoubleBedPer = 0)
BEGIN
	SET @TaxFreeAmount = @SingleTotal + @DoubleTotal  
END
ELSE if(@SingleBedPer = 12 and @DoubleBedPer = 12)
BEGIN
	SET @SlabOneAmount = @SingleTotal + @DoubleTotal 
	SET @SlabOneTax = @SingleBedPercentAmount + @DoubleBedPercentAmount
END
ELSE if(@SingleBedPer = 18 and @DoubleBedPer = 18)
BEGIN
	SET @SlabTwoAmount = @SingleTotal + @DoubleTotal
	SET @SlabTwoTax = @SingleBedPercentAmount + @DoubleBedPercentAmount
END
ELSE if(@SingleBedPer = 28 and @DoubleBedPer = 28)
BEGIN
	SET @SlabThreeAmount = @SingleTotal + @DoubleTotal
	SET @SlabThreeTax = @SingleBedPercentAmount + @DoubleBedPercentAmount
END
ELSE
BEGIN
	IF(@SingleBedPer = 0 )
	BEGIN
		SET @SlabOneAmount = @SingleTotal 
		SET @SlabOneTax = @SingleBedPercentAmount
	END
	ELSE IF(@SingleBedPer = 12 )
	BEGIN
		SET @SlabTwoAmount = @SingleTotal 
		SET @SlabTwoTax = @SingleBedPercentAmount 
	END
	ELSE IF(@SingleBedPer = 18 )
	BEGIN
		SET @SlabTwoAmount = @SingleTotal 
		SET @SlabTwoTax = @SingleBedPercentAmount 
	END
	ELSE IF(@SingleBedPer = 28 )
	BEGIN
		SET @SlabThreeAmount = @SingleTotal 
		SET @SlabThreeTax = @SingleBedPercentAmount
	END
	
	IF(@DoubleBedPer = 0 )
	BEGIN
		SET @SlabOneAmount = @DoubleTotal 
		SET @SlabOneTax = @DoubleBedPercentAmount
	END
	ELSE IF(@DoubleBedPer = 12 )
	BEGIN
		SET @SlabTwoAmount = @DoubleTotal 
		SET @SlabTwoTax = @DoubleBedPercentAmount 
	END
	ELSE IF(@DoubleBedPer = 18 )
	BEGIN
		SET @SlabTwoAmount = @DoubleTotal 
		SET @SlabTwoTax = @DoubleBedPercentAmount 
	END
	ELSE IF(@DoubleBedPer = 28 )
	BEGIN
		SET @SlabThreeAmount = @DoubleTotal 
		SET @SlabThreeTax = @DoubleBedPercentAmount
	END	
END
SELECT @TaxFreeAmount TaxFreeAmount,@SlabOneAmount 	SlabOneAmount,@SlabOneTax labOneTax,@SlabTwoAmount SlabTwoAmount,@SlabTwoTax SlabTwoTax,@SlabThreeAmount SlabThreeAmount,@SlabThreeTax SlabThreeTax
Screenshot
| TaxFreeAmount | SlabOneAmount | labOneTax | SlabTwoAmount | SlabTwoTax | SlabThreeAmount | SlabThreeTax | 
| 0.00 | 300.00 | 36.00 | 0.00 | 0.00 | 0.00 | 0.00 |