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	$150.67	5.456%	$158.8906	$158.89	$158.90	$158.90
Purchase #2	$120.42	6.865%	$128.6868	$128.69	$128.70	$128.70
Purchase #3	$50.33	8.716%	$54.7168	$54.72	$54.70	$54.70
Purchase #4	$122.77	4.510%	$128.3069	$128.31	$128.30	$128.30
Purchase #5	$62.74	7.320%	$67.3326	$67.33	$67.35	$67.30
Purchase #6	$71.34	13.754%	$81.1521	$81.15	$81.15	$81.20
Purchase #7	$125.85	9.120%	$137.3275	$137.33	$137.35	$137.30
7 purchase totals =	$704.12		$756.4133	$756.42	$756.45	$756.40