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	$201.88	9.683%	$221.428	$221.43	$221.45	$221.40
Purchase #2	$155.79	10.748%	$172.5343	$172.53	$172.55	$172.50
Purchase #3	$229.26	11.737%	$256.1682	$256.17	$256.15	$256.20
Purchase #4	$206.82	3.828%	$214.7371	$214.74	$214.75	$214.70
Purchase #5	$135.36	3.386%	$139.9433	$139.94	$139.95	$139.90
Purchase #6	$40.87	11.111%	$45.4111	$45.41	$45.40	$45.40
Purchase #7	$180.87	13.567%	$205.4086	$205.41	$205.40	$205.40
7 purchase totals =	$1,150.85		$1,255.6306	$1,255.63	$1,255.65	$1,255.50