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	$59.82	9.621%	$65.5753	$65.58	$65.60	$65.60
Purchase #2	$233.74	5.518%	$246.6378	$246.64	$246.65	$246.60
Purchase #3	$137.78	9.599%	$151.0055	$151.01	$151.00	$151.00
Purchase #4	$139.85	8.328%	$151.4967	$151.50	$151.50	$151.50
Purchase #5	$88.31	8.481%	$95.7996	$95.80	$95.80	$95.80
Purchase #6	$59.74	9.568%	$65.4559	$65.46	$65.45	$65.50
Purchase #7	$84.46	7.489%	$90.7852	$90.79	$90.80	$90.80
7 purchase totals =	$803.70		$866.7560	$866.78	$866.80	$866.80