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	$9.88	8.290%	$10.6991	$10.70	$10.70	$10.70
Purchase #2	$104.85	6.312%	$111.4681	$111.47	$111.45	$111.50
Purchase #3	$218.45	10.335%	$241.0268	$241.03	$241.05	$241.00
Purchase #4	$114.59	5.735%	$121.1617	$121.16	$121.15	$121.20
Purchase #5	$160.36	7.462%	$172.3261	$172.33	$172.35	$172.30
Purchase #6	$157.87	4.282%	$164.63	$164.63	$164.65	$164.60
Purchase #7	$246.36	7.751%	$265.4554	$265.46	$265.45	$265.50
7 purchase totals =	$1,012.36		$1,086.7672	$1,086.78	$1,086.80	$1,086.80