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	$7.94	11.587%	$8.86	$8.86	$8.85	$8.90
Purchase #2	$46.90	12.500%	$52.7625	$52.76	$52.75	$52.80
Purchase #3	$111.75	4.319%	$116.5765	$116.58	$116.60	$116.60
Purchase #4	$125.83	6.339%	$133.8064	$133.81	$133.80	$133.80
Purchase #5	$201.70	13.263%	$228.4515	$228.45	$228.45	$228.50
Purchase #6	$221.46	13.745%	$251.8997	$251.90	$251.90	$251.90
Purchase #7	$64.28	5.646%	$67.9092	$67.91	$67.90	$67.90
7 purchase totals =	$779.86		$860.2658	$860.27	$860.25	$860.40