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	$100.51	11.106%	$111.6726	$111.67	$111.65	$111.70
Purchase #2	$113.52	10.473%	$125.4089	$125.41	$125.40	$125.40
Purchase #3	$111.25	10.773%	$123.235	$123.24	$123.25	$123.20
Purchase #4	$115.30	7.302%	$123.7192	$123.72	$123.70	$123.70
Purchase #5	$47.89	4.723%	$50.1518	$50.15	$50.15	$50.20
Purchase #6	$66.39	7.815%	$71.5784	$71.58	$71.60	$71.60
Purchase #7	$18.64	6.262%	$19.8072	$19.81	$19.80	$19.80
7 purchase totals =	$573.50		$625.5731	$625.58	$625.55	$625.60