The advantage of the cashier position is its ubiquity. The jobs are in retail, grocery stores, department stores, gas stations, fast food, etc. You can get a job in almost any field and any geographic area.
Bookkeepers perform accounting functions for small businesses. They create and track invoices to customers, do payroll for employees and independent contractors, maintain financial records, and pay invoices from suppliers.
Almost all dental hygienists work in dentists or other oral care offices. You will perform oral preventative care and check for oral diseases like gingivitis and cavities. The advantage is that the position has reasonable working hours.