Workers can be put under tremendous pressure to pick up the tab for losses which are not their fault - by being threatened with dismissal for example.
Such deductions are only lawful if there is a specific term in the contract of employment permitting the employer to do so. You must be given a written copy of that term so that you know your liability in the event of till shortages, and the deductions must not exceed 10% of your gross pay packet unless it is your final pay packet.