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	$230.80	6.734%	$246.3421	$246.34	$246.35	$246.30
Purchase #2	$184.53	9.337%	$201.7596	$201.76	$201.75	$201.80
Purchase #3	$107.47	4.676%	$112.4953	$112.50	$112.50	$112.50
Purchase #4	$94.51	10.650%	$104.5753	$104.58	$104.60	$104.60
Purchase #5	$57.51	7.480%	$61.8117	$61.81	$61.80	$61.80
Purchase #6	$65.59	3.466%	$67.8633	$67.86	$67.85	$67.90
Purchase #7	$67.50	13.289%	$76.4701	$76.47	$76.45	$76.50
7 purchase totals =	$807.91		$871.3174	$871.32	$871.30	$871.40