Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$130.47	5.663%	$137.8585	$137.86	$137.85	$137.90
Purchase #2	$48.87	10.115%	$53.8132	$53.81	$53.80	$53.80
Purchase #3	$155.55	8.543%	$168.8386	$168.84	$168.85	$168.80
Purchase #4	$142.96	3.839%	$148.4482	$148.45	$148.45	$148.40
Purchase #5	$145.67	7.134%	$156.0621	$156.06	$156.05	$156.10
Purchase #6	$134.78	3.843%	$139.9596	$139.96	$139.95	$140.00
Purchase #7	$184.53	3.777%	$191.4997	$191.50	$191.50	$191.50
7 purchase totals =	$942.83		$996.4799	$996.48	$996.45	$996.50