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	$7.65	3.419%	$7.9116	$7.91	$7.90	$7.90
Purchase #2	$134.95	12.443%	$151.7418	$151.74	$151.75	$151.70
Purchase #3	$77.62	11.252%	$86.3538	$86.35	$86.35	$86.40
Purchase #4	$204.35	5.313%	$215.2071	$215.21	$215.20	$215.20
Purchase #5	$27.31	12.249%	$30.6552	$30.66	$30.65	$30.70
Purchase #6	$53.52	11.167%	$59.4966	$59.50	$59.50	$59.50
Purchase #7	$39.95	5.504%	$42.1488	$42.15	$42.15	$42.10
7 purchase totals =	$545.35		$593.5149	$593.52	$593.50	$593.50