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	$49.70	12.732%	$56.0278	$56.03	$56.05	$56.00
Purchase #2	$93.91	12.213%	$105.3792	$105.38	$105.40	$105.40
Purchase #3	$169.66	13.303%	$192.2299	$192.23	$192.25	$192.20
Purchase #4	$246.92	3.435%	$255.4017	$255.40	$255.40	$255.40
Purchase #5	$37.84	13.191%	$42.8315	$42.83	$42.85	$42.80
Purchase #6	$64.74	10.576%	$71.5869	$71.59	$71.60	$71.60
Purchase #7	$227.49	3.504%	$235.4612	$235.46	$235.45	$235.50
7 purchase totals =	$890.26		$958.9182	$958.92	$959.00	$958.90