Yes, you can sue both the at-fault employee and the auto parts store for the cost to repair your car (if it can be repaired) or the then-current value of the car (its value when it was destroyed), if the car's value at that time was less than the cost to repair. (They have to pay the lesser of the repair cost or fair market value.) They do not have to pay the cost of a new car--it's repair or value of the car that was destroyed. Any person who negligently (or carelessly) damages or destroys another's property can be liable for it; and if the damage is done in the course of that person's employment, his or her employer can be liable, too, under the theory of "respondeat superior."