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	$144.51	8.268%	$156.4581	$156.46	$156.45	$156.50
Purchase #2	$248.72	8.601%	$270.1124	$270.11	$270.10	$270.10
Purchase #3	$85.77	11.513%	$95.6447	$95.64	$95.65	$95.60
Purchase #4	$38.33	12.522%	$43.1297	$43.13	$43.15	$43.10
Purchase #5	$84.62	7.481%	$90.9504	$90.95	$90.95	$91.00
Purchase #6	$44.98	8.540%	$48.8213	$48.82	$48.80	$48.80
Purchase #7	$7.89	4.679%	$8.2592	$8.26	$8.25	$8.30
7 purchase totals =	$654.82		$713.3758	$713.37	$713.35	$713.40