Try the following Script

SELECT PercRate, Amount, Code

INTO #TestValues

FROM (

SELECT 6.00 PercRate , 172715 Amount , 13 Code UNION ALL

SELECT 6.50, 172716, 13 UNION ALL

SELECT 7.00, 181351, 13 UNION ALL

SELECT 7.50, 190419, 13 UNION ALL

SELECT 6.00, 200000, 18 UNION ALL

SELECT 6.50, 200100, 18 UNION ALL

SELECT 7.00, 200200, 18 UNION ALL

SELECT 7.50, 200300, 18 UNION ALL

SELECT 6.00, 0, 21 UNION ALL

SELECT 6.50, 1, 21

) d

SELECT GMAdj, Payment, Code

INTO #SM

FROM (

SELECT 171314.36, 909, 13 UNION ALL

SELECT 200299, 500, 18

) d ( GMAdj, Payment, Code);

SELECT

PercRate, Amount, Code,GMAdj,Payment

FROM

(

SELECT

PercRate, Amount, #TestValues.Code,GMAdj,Payment,ROW_NUMBER() OVER(Partition By GMAdj Order by ABS((GMAdj-Amount)) ASC) AS RID

from

#TestValues

INNER JOIN #SM ON #SM.Code = #TestValues.Code

)X

WHERE RID = 1

DROP TABLE #TestValues

DROP TABLE #SM