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	$33.99	10.584%	$37.5875	$37.59	$37.60	$37.60
Purchase #2	$149.79	4.511%	$156.547	$156.55	$156.55	$156.50
Purchase #3	$139.47	6.447%	$148.4616	$148.46	$148.45	$148.50
Purchase #4	$42.85	5.152%	$45.0576	$45.06	$45.05	$45.10
Purchase #5	$95.95	6.462%	$102.1503	$102.15	$102.15	$102.20
Purchase #6	$156.80	5.723%	$165.7737	$165.77	$165.75	$165.80
Purchase #7	$122.49	7.230%	$131.346	$131.35	$131.35	$131.30
7 purchase totals =	$741.34		$786.9237	$786.93	$786.90	$787.00