:( :( okay is it legal for a manager/ owner of a retail store to deduct shift shortages from your paycheck? :(

Not without your written authorization.

Under Tennessee law deductions can only be taken out of pay if the employee has authorized it by a written statement.
http://www.state.tn.us/labor-wfd/lsques.html#laborlaws

This, of course, does not include taxes or other deductions required by law (such as child support or garnishments).