In most of Europe, it is illegal to pay differently for equal work, so a female cashier would be paid the same as a male cashier.
The gap arises where men are able to take more hours, obtain more qualifications, develop more experience, enter more lucrative industries, get more promotions & they are far less likely to leave paid employment to raise children.
Some of that is due to personal choice, which is fine, but most of it is down to societal hurdles outside of work which determine how women approach the workplace.