If it's just something you're putting on CV for first-year results, i.e. informal, it would be most reasonable to round it up.
Some unis have peculiarly strict practices where they will treat such grades as less than 70% and the only way you can get it up to a first is if the board of examiners exercise discretion -- this is only in relation to formal classification, so not relevant here. Your uni should say in the regs what their rules are, if you're curious.