Pretty sure my local tackle dealer uses a calculator too, but he's not exactly big time. In this day and age you expect all shops to use a till of some description, but an all-singing, all-dancing EPOS systemwith barcode scanner etc etcis a capital expenditure not all tackle dealers can justify.
As fortills being a legal requirement, what's the difference between a retailerwith shop premises anda trader selling his wares ona market stall? Plenty of market traders are VAT registered (I also acceptplenty aren't!!) but most of those won'thave accessto a till. They or an accountant do theirbooks, theirtax returns etc. and I think its down to taxman to theninvestigate/audit if he thinks there's something untoward.