Yes, it's legal for an employer to send you home early as often as he wishes/needs to unless you have a bona fide employment contract to the contrary. However, in NJ your employer is required to pay you for an hour of your scheduled shift if you are sent home before an hr. is up. It looks like you work longer than that though so you would get paid for the amount of time you actually work. I assume you are hourly non-exempt employees.
An exempt employee would get paid their regular weekly salary no matter how many hrs. a week they work with some exceptions.

