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	$214.28	4.861%	$224.6962	$224.70	$224.70	$224.70
Purchase #2	$173.83	9.657%	$190.6168	$190.62	$190.60	$190.60
Purchase #3	$170.39	8.652%	$185.1321	$185.13	$185.15	$185.10
Purchase #4	$53.71	7.652%	$57.8199	$57.82	$57.80	$57.80
Purchase #5	$95.34	10.333%	$105.1915	$105.19	$105.20	$105.20
Purchase #6	$133.84	7.136%	$143.3908	$143.39	$143.40	$143.40
Purchase #7	$100.86	13.588%	$114.5649	$114.56	$114.55	$114.60
7 purchase totals =	$942.25		$1,021.4122	$1,021.41	$1,021.40	$1,021.40