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	$57.67	3.325%	$59.5875	$59.59	$59.60	$59.60
Purchase #2	$152.46	4.710%	$159.6409	$159.64	$159.65	$159.60
Purchase #3	$171.62	5.301%	$180.7176	$180.72	$180.70	$180.70
Purchase #4	$225.80	9.594%	$247.4633	$247.46	$247.45	$247.50
Purchase #5	$18.69	8.233%	$20.2287	$20.23	$20.25	$20.20
Purchase #6	$184.78	11.602%	$206.2182	$206.22	$206.20	$206.20
Purchase #7	$38.79	8.158%	$41.9545	$41.95	$41.95	$42.00
7 purchase totals =	$849.81		$915.8107	$915.81	$915.80	$915.80