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	$224.35	13.782%	$255.2699	$255.27	$255.25	$255.30
Purchase #2	$90.97	10.315%	$100.3536	$100.35	$100.35	$100.40
Purchase #3	$126.66	9.792%	$139.0625	$139.06	$139.05	$139.10
Purchase #4	$133.67	13.287%	$151.4307	$151.43	$151.45	$151.40
Purchase #5	$69.47	7.613%	$74.7588	$74.76	$74.75	$74.80
Purchase #6	$247.60	4.800%	$259.4848	$259.48	$259.50	$259.50
Purchase #7	$176.69	10.497%	$195.2371	$195.24	$195.25	$195.20
7 purchase totals =	$1,069.41		$1,175.5974	$1,175.59	$1,175.60	$1,175.70