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	$155.39	6.314%	$165.2013	$165.20	$165.20	$165.20
Purchase #2	$50.50	5.492%	$53.2735	$53.27	$53.25	$53.30
Purchase #3	$148.86	13.757%	$169.3387	$169.34	$169.35	$169.30
Purchase #4	$229.67	13.157%	$259.8877	$259.89	$259.90	$259.90
Purchase #5	$92.43	9.192%	$100.9262	$100.93	$100.95	$100.90
Purchase #6	$21.81	12.340%	$24.5014	$24.50	$24.50	$24.50
Purchase #7	$44.91	8.256%	$48.6178	$48.62	$48.60	$48.60
7 purchase totals =	$743.57		$821.7466	$821.75	$821.75	$821.70