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	$247.76	3.308%	$255.9559	$255.96	$255.95	$256.00
Purchase #2	$143.92	7.800%	$155.1458	$155.15	$155.15	$155.10
Purchase #3	$163.32	13.813%	$185.8794	$185.88	$185.90	$185.90
Purchase #4	$37.72	3.260%	$38.9497	$38.95	$38.95	$38.90
Purchase #5	$213.54	5.433%	$225.1416	$225.14	$225.15	$225.10
Purchase #6	$70.76	11.863%	$79.1543	$79.15	$79.15	$79.20
Purchase #7	$18.37	5.537%	$19.3871	$19.39	$19.40	$19.40
7 purchase totals =	$895.39		$959.6138	$959.62	$959.65	$959.60