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	$133.54	7.475%	$143.5221	$143.52	$143.50	$143.50
Purchase #2	$192.79	12.369%	$216.6362	$216.64	$216.65	$216.60
Purchase #3	$244.32	10.196%	$269.2309	$269.23	$269.25	$269.20
Purchase #4	$173.79	6.627%	$185.3071	$185.31	$185.30	$185.30
Purchase #5	$60.59	8.846%	$65.9498	$65.95	$65.95	$65.90
Purchase #6	$239.29	11.422%	$266.6217	$266.62	$266.60	$266.60
Purchase #7	$220.32	10.211%	$242.8169	$242.82	$242.80	$242.80
7 purchase totals =	$1,264.64		$1,390.0847	$1,390.09	$1,390.05	$1,389.90