If you measure in 1/8ths there'd be no reason to "round off".
You are to measure to the nearest 1/8. For example, if a tinemeasures 5 3/16's long you would round up to 5 1/4. If the tine was just short of 5 3/16 you would mark the measurement down as 5 1/8. So basically, like previously mentioned round to the nearest 1/8.