Well, lets figure out how much 5% is as a decimal. 5% as a decimal is 0.05. Now, lets multiply 51.70 by 0.05 so we figure out how much that tax is. His tax would be 2.585, but because its money we have to round to the nearest hundredth, making it 2.59. Now, because we know how much his tax is lets add it. His total would be 54.285, 54.29 to be exact.