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	$27.36	8.634%	$29.7223	$29.72	$29.70	$29.70
Purchase #2	$40.62	4.655%	$42.5109	$42.51	$42.50	$42.50
Purchase #3	$132.94	13.813%	$151.303	$151.30	$151.30	$151.30
Purchase #4	$38.90	5.102%	$40.8847	$40.88	$40.90	$40.90
Purchase #5	$163.85	5.451%	$172.7815	$172.78	$172.80	$172.80
Purchase #6	$95.94	10.552%	$106.0636	$106.06	$106.05	$106.10
Purchase #7	$218.48	4.424%	$228.1456	$228.15	$228.15	$228.10
7 purchase totals =	$718.09		$771.4116	$771.40	$771.40	$771.40