Is it always a good idea to choose $0\%$ financing? What about cash$-$back deals?

For example, during the purchase of a vehicle you are able to choose from the

following:

$0\%$ financing

R$-$

$5\%$ financing with $$2000$ cash back

Please note. it is common practice to take the cash back amount and apply it to

the principal of the loan, therefore reducing the amount financed.

So$,$ if you purchased a vehicle with a $$20,000$ purchase price, using method $1$ you

would be paying $$20,000$ at $0\%$ or just $$20,000$ overall. With method $2,$ you

would be paying off $$18,000$ at $5\%......$

Is there ever a combination of interest rate$/$amount of cash back that would make

$0\%$ interest the bad choice?