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	$93.53	11.724%	$104.4955	$104.50	$104.50	$104.50
Purchase #2	$129.41	11.172%	$143.8677	$143.87	$143.85	$143.90
Purchase #3	$42.72	10.453%	$47.1855	$47.19	$47.20	$47.20
Purchase #4	$220.33	8.316%	$238.6526	$238.65	$238.65	$238.70
Purchase #5	$105.86	9.660%	$116.0861	$116.09	$116.10	$116.10
Purchase #6	$70.87	10.532%	$78.334	$78.33	$78.35	$78.30
Purchase #7	$67.75	9.181%	$73.9701	$73.97	$73.95	$74.00
7 purchase totals =	$730.47		$802.5915	$802.60	$802.60	$802.70