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	$240.72	5.196%	$253.2278	$253.23	$253.25	$253.20
Purchase #2	$67.86	13.341%	$76.9132	$76.91	$76.90	$76.90
Purchase #3	$203.52	13.790%	$231.5854	$231.59	$231.60	$231.60
Purchase #4	$245.97	3.152%	$253.723	$253.72	$253.70	$253.70
Purchase #5	$48.28	12.615%	$54.3705	$54.37	$54.35	$54.40
Purchase #6	$143.56	11.626%	$160.2503	$160.25	$160.25	$160.30
Purchase #7	$56.81	6.788%	$60.6663	$60.67	$60.65	$60.70
7 purchase totals =	$1,006.72		$1,090.7365	$1,090.74	$1,090.70	$1,090.80