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	$14.27	13.413%	$16.184	$16.18	$16.20	$16.20
Purchase #2	$10.48	9.500%	$11.4756	$11.48	$11.50	$11.50
Purchase #3	$94.70	5.456%	$99.8668	$99.87	$99.85	$99.90
Purchase #4	$50.69	6.173%	$53.8191	$53.82	$53.80	$53.80
Purchase #5	$152.67	4.729%	$159.8898	$159.89	$159.90	$159.90
Purchase #6	$210.47	6.188%	$223.4939	$223.49	$223.50	$223.50
Purchase #7	$107.51	3.300%	$111.0578	$111.06	$111.05	$111.10
7 purchase totals =	$640.79		$675.7870	$675.79	$675.80	$675.90