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	$159.84	4.166%	$166.4989	$166.50	$166.50	$166.50
Purchase #2	$213.49	6.253%	$226.8395	$226.84	$226.85	$226.80
Purchase #3	$41.72	5.852%	$44.1615	$44.16	$44.15	$44.20
Purchase #4	$55.32	8.187%	$59.849	$59.85	$59.85	$59.80
Purchase #5	$230.32	9.391%	$251.9494	$251.95	$251.95	$251.90
Purchase #6	$21.65	4.389%	$22.6002	$22.60	$22.60	$22.60
Purchase #7	$99.75	11.807%	$111.5275	$111.53	$111.55	$111.50
7 purchase totals =	$822.09		$883.4260	$883.43	$883.45	$883.30