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	$16.35	12.314%	$18.3633	$18.36	$18.35	$18.40
Purchase #2	$120.61	5.790%	$127.5933	$127.59	$127.60	$127.60
Purchase #3	$94.90	5.178%	$99.8139	$99.81	$99.80	$99.80
Purchase #4	$214.99	9.189%	$234.7454	$234.75	$234.75	$234.70
Purchase #5	$226.75	13.272%	$256.8443	$256.84	$256.85	$256.80
Purchase #6	$202.67	4.472%	$211.7334	$211.73	$211.75	$211.70
Purchase #7	$92.89	13.649%	$105.5686	$105.57	$105.55	$105.60
7 purchase totals =	$969.16		$1,054.6622	$1,054.65	$1,054.65	$1,054.60