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	$243.60	11.490%	$271.5896	$271.59	$271.60	$271.60
Purchase #2	$67.72	9.307%	$74.0227	$74.02	$74.00	$74.00
Purchase #3	$93.95	6.136%	$99.7148	$99.71	$99.70	$99.70
Purchase #4	$12.64	9.586%	$13.8517	$13.85	$13.85	$13.90
Purchase #5	$91.49	9.395%	$100.0855	$100.09	$100.10	$100.10
Purchase #6	$50.96	4.207%	$53.1039	$53.10	$53.10	$53.10
Purchase #7	$225.92	13.640%	$256.7355	$256.74	$256.75	$256.70
7 purchase totals =	$786.28		$869.1037	$869.10	$869.10	$869.10