Kingtim Co AFM Specimen from Sep 2022 onwards

Sir, while calculating the post-tax cost of debt of the new bond using IRR, instead of calculating the post-tax interest and then applying IRR on that, can we instead calculate IRR on the pre-tax interest and then multiply this by (1-t) to get the post-tax cost of debt? In this case, I get the answer as 4.8% instead of 4.76% as provided in the answer key. Would this still be correct sir?