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	$239.98	6.331%	$255.1731	$255.17	$255.15	$255.20
Purchase #2	$82.85	11.841%	$92.6603	$92.66	$92.65	$92.70
Purchase #3	$57.76	4.852%	$60.5625	$60.56	$60.55	$60.60
Purchase #4	$27.82	4.388%	$29.0407	$29.04	$29.05	$29.00
Purchase #5	$107.76	7.827%	$116.1944	$116.19	$116.20	$116.20
Purchase #6	$22.68	7.178%	$24.308	$24.31	$24.30	$24.30
Purchase #7	$74.44	10.864%	$82.5272	$82.53	$82.55	$82.50
7 purchase totals =	$613.29		$660.4662	$660.46	$660.45	$660.50