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	$78.38	10.643%	$86.722	$86.72	$86.70	$86.70
Purchase #2	$111.31	3.189%	$114.8597	$114.86	$114.85	$114.90
Purchase #3	$94.51	6.487%	$100.6409	$100.64	$100.65	$100.60
Purchase #4	$208.67	3.690%	$216.3699	$216.37	$216.35	$216.40
Purchase #5	$13.43	12.363%	$15.0904	$15.09	$15.10	$15.10
Purchase #6	$73.27	10.835%	$81.2088	$81.21	$81.20	$81.20
Purchase #7	$57.55	7.344%	$61.7765	$61.78	$61.80	$61.80
7 purchase totals =	$637.12		$676.6682	$676.67	$676.65	$676.70