Sure you can, however that would not be entirely effective as your cabin is still being exposed to UV rays and heat from other exposed windows. If cost is a factor and you still want the required protection, we recommend doing at least the bare minimum of tinting the front 3 panels (front windscreen, driver side and passenger side windows).
That said – tinting the entire cabin makes for a drastically different feeling especially if your car is parked in the sun for a while. Your rear dashboard (area behind the rear passenger seats) soaks and retains a lot of heat if your rear windows are not tinted. We regularly see returning customers tint the rear of the car when they’ve only done the front 3 at first.