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	$78.53	5.527%	$82.8704	$82.87	$82.85	$82.90
Purchase #2	$47.43	3.260%	$48.9762	$48.98	$49.00	$49.00
Purchase #3	$127.50	3.855%	$132.4151	$132.42	$132.40	$132.40
Purchase #4	$100.86	10.633%	$111.5844	$111.58	$111.60	$111.60
Purchase #5	$16.41	7.642%	$17.6641	$17.66	$17.65	$17.70
Purchase #6	$203.33	3.634%	$210.719	$210.72	$210.70	$210.70
Purchase #7	$48.41	13.135%	$54.7687	$54.77	$54.75	$54.80
7 purchase totals =	$622.47		$658.9979	$659.00	$658.95	$659.10