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	$151.93	6.138%	$161.2555	$161.26	$161.25	$161.30
Purchase #2	$38.51	10.521%	$42.5616	$42.56	$42.55	$42.60
Purchase #3	$58.98	12.868%	$66.5695	$66.57	$66.55	$66.60
Purchase #4	$98.98	13.835%	$112.6739	$112.67	$112.65	$112.70
Purchase #5	$36.33	4.820%	$38.0811	$38.08	$38.10	$38.10
Purchase #6	$54.64	13.547%	$62.0421	$62.04	$62.05	$62.00
Purchase #7	$104.44	4.749%	$109.3999	$109.40	$109.40	$109.40
7 purchase totals =	$543.81		$592.5836	$592.58	$592.55	$592.70