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	$90.50	13.182%	$102.4297	$102.43	$102.45	$102.40
Purchase #2	$37.29	8.521%	$40.4675	$40.47	$40.45	$40.50
Purchase #3	$239.25	13.429%	$271.3789	$271.38	$271.40	$271.40
Purchase #4	$177.32	11.653%	$197.9831	$197.98	$198.00	$198.00
Purchase #5	$34.68	11.253%	$38.5825	$38.58	$38.60	$38.60
Purchase #6	$11.68	6.805%	$12.4748	$12.47	$12.45	$12.50
Purchase #7	$137.40	10.401%	$151.691	$151.69	$151.70	$151.70
7 purchase totals =	$728.12		$815.0075	$815.00	$815.05	$815.10