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	$27.66	3.487%	$28.6245	$28.62	$28.60	$28.60
Purchase #2	$155.94	10.629%	$172.5149	$172.51	$172.50	$172.50
Purchase #3	$40.71	3.450%	$42.1145	$42.11	$42.10	$42.10
Purchase #4	$121.51	13.612%	$138.0499	$138.05	$138.05	$138.00
Purchase #5	$237.69	10.829%	$263.4295	$263.43	$263.45	$263.40
Purchase #6	$235.52	4.752%	$246.7119	$246.71	$246.70	$246.70
Purchase #7	$169.37	12.578%	$190.6734	$190.67	$190.65	$190.70
7 purchase totals =	$988.40		$1,082.1186	$1,082.10	$1,082.05	$1,082.00