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	$34.35	13.499%	$38.9869	$38.99	$39.00	$39.00
Purchase #2	$167.81	13.409%	$190.3116	$190.31	$190.30	$190.30
Purchase #3	$10.64	4.382%	$11.1062	$11.11	$11.10	$11.10
Purchase #4	$129.38	11.684%	$144.4968	$144.50	$144.50	$144.50
Purchase #5	$189.33	5.626%	$199.9817	$199.98	$200.00	$200.00
Purchase #6	$103.75	12.758%	$116.9864	$116.99	$117.00	$117.00
Purchase #7	$105.78	5.351%	$111.4403	$111.44	$111.45	$111.40
7 purchase totals =	$741.04		$813.3099	$813.32	$813.35	$813.30