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	$137.79	12.556%	$155.0909	$155.09	$155.10	$155.10
Purchase #2	$25.88	8.303%	$28.0288	$28.03	$28.05	$28.00
Purchase #3	$191.66	3.604%	$198.5674	$198.57	$198.55	$198.60
Purchase #4	$50.67	5.521%	$53.4675	$53.47	$53.45	$53.50
Purchase #5	$173.36	9.841%	$190.4204	$190.42	$190.40	$190.40
Purchase #6	$126.94	12.790%	$143.1756	$143.18	$143.20	$143.20
Purchase #7	$127.52	11.132%	$141.7155	$141.72	$141.70	$141.70
7 purchase totals =	$833.82		$910.4661	$910.48	$910.45	$910.50