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	$140.83	7.522%	$151.4232	$151.42	$151.40	$151.40
Purchase #2	$216.91	6.227%	$230.417	$230.42	$230.40	$230.40
Purchase #3	$194.89	8.586%	$211.6233	$211.62	$211.60	$211.60
Purchase #4	$105.28	11.754%	$117.6546	$117.65	$117.65	$117.70
Purchase #5	$218.39	4.256%	$227.6847	$227.68	$227.70	$227.70
Purchase #6	$58.42	5.106%	$61.4029	$61.40	$61.40	$61.40
Purchase #7	$79.86	12.222%	$89.6205	$89.62	$89.60	$89.60
7 purchase totals =	$1,014.58		$1,089.8262	$1,089.81	$1,089.75	$1,089.80