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	$26.58	13.470%	$30.1603	$30.16	$30.15	$30.20
Purchase #2	$230.31	11.465%	$256.715	$256.72	$256.70	$256.70
Purchase #3	$151.74	10.584%	$167.8002	$167.80	$167.80	$167.80
Purchase #4	$167.82	6.857%	$179.3274	$179.33	$179.35	$179.30
Purchase #5	$245.27	12.455%	$275.8184	$275.82	$275.80	$275.80
Purchase #6	$47.44	13.803%	$53.9881	$53.99	$54.00	$54.00
Purchase #7	$192.57	8.476%	$208.8922	$208.89	$208.90	$208.90
7 purchase totals =	$1,061.73		$1,172.7016	$1,172.71	$1,172.70	$1,172.70