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	$54.96	6.726%	$58.6566	$58.66	$58.65	$58.70
Purchase #2	$42.83	6.766%	$45.7279	$45.73	$45.75	$45.70
Purchase #3	$176.51	8.454%	$191.4322	$191.43	$191.45	$191.40
Purchase #4	$66.85	8.835%	$72.7562	$72.76	$72.75	$72.80
Purchase #5	$106.49	7.626%	$114.6109	$114.61	$114.60	$114.60
Purchase #6	$13.99	3.791%	$14.5204	$14.52	$14.50	$14.50
Purchase #7	$63.59	10.313%	$70.148	$70.15	$70.15	$70.10
7 purchase totals =	$525.22		$567.8522	$567.86	$567.85	$567.80