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	$189.93	10.453%	$209.7834	$209.78	$209.80	$209.80
Purchase #2	$60.46	13.354%	$68.5338	$68.53	$68.55	$68.50
Purchase #3	$25.30	6.288%	$26.8909	$26.89	$26.90	$26.90
Purchase #4	$55.27	11.290%	$61.51	$61.51	$61.50	$61.50
Purchase #5	$214.88	4.112%	$223.7159	$223.72	$223.70	$223.70
Purchase #6	$143.54	11.124%	$159.5074	$159.51	$159.50	$159.50
Purchase #7	$53.43	13.315%	$60.5442	$60.54	$60.55	$60.50
7 purchase totals =	$742.81		$810.4856	$810.48	$810.50	$810.40