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	$111.68	10.716%	$123.6476	$123.65	$123.65	$123.60
Purchase #2	$204.86	8.417%	$222.1031	$222.10	$222.10	$222.10
Purchase #3	$183.90	6.663%	$196.1533	$196.15	$196.15	$196.20
Purchase #4	$199.50	12.313%	$224.0644	$224.06	$224.05	$224.10
Purchase #5	$119.59	3.713%	$124.0304	$124.03	$124.05	$124.00
Purchase #6	$32.91	5.773%	$34.8099	$34.81	$34.80	$34.80
Purchase #7	$40.44	13.424%	$45.8687	$45.87	$45.85	$45.90
7 purchase totals =	$892.88		$970.6774	$970.67	$970.65	$970.70