Reversal of cenvat credit

Which rates applicable for reversal of cenvat credit 10.30% or 12.36%,

Cenvat credit availed in the month of March 2012 on the Bill of Rs 10000 on which Rs 1030 s.tax,but due to some reason we get the Credit Note from the vendor in the month of May 2012 of Rs 10000 on which vendor  calculate S.Tax @ 12.36% .

is this  correct to calculate S.Tax 12.36% on credit note raised in the month May 2012 which relates to Mar 2012 ?