As I said an another siimilar thread recently, it's the software behind the shopping trolly that's the culprit, unless they have paid a lot of money for a high-end product it will only recognise whole units. So, if the unit is designated as 1 m they can only sell in whole metres, if the designated unit is 0.5 metres they can sell in half metres but the unit price has to be half of the cost per metre. That's OK if the general blurb makes it clear and says something like £4.99 per half metre = £9.98 per metre.
Ideally they should be selling in units of 0.25m or better still units of 0.1m (maybe with a minimum cut).