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	$23.58	4.240%	$24.5798	$24.58	$24.60	$24.60
Purchase #2	$244.87	5.716%	$258.8668	$258.87	$258.85	$258.90
Purchase #3	$176.79	8.195%	$191.2779	$191.28	$191.30	$191.30
Purchase #4	$211.44	10.858%	$234.3982	$234.40	$234.40	$234.40
Purchase #5	$46.39	4.680%	$48.5611	$48.56	$48.55	$48.60
Purchase #6	$66.70	9.246%	$72.8671	$72.87	$72.85	$72.90
Purchase #7	$249.77	7.538%	$268.5977	$268.60	$268.60	$268.60
7 purchase totals =	$1,019.54		$1,099.1486	$1,099.16	$1,099.15	$1,099.30