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	$122.83	10.845%	$136.1509	$136.15	$136.15	$136.20
Purchase #2	$134.60	4.742%	$140.9827	$140.98	$141.00	$141.00
Purchase #3	$241.31	11.676%	$269.4854	$269.49	$269.50	$269.50
Purchase #4	$49.36	8.715%	$53.6617	$53.66	$53.65	$53.70
Purchase #5	$222.53	8.699%	$241.8879	$241.89	$241.90	$241.90
Purchase #6	$89.40	5.315%	$94.1516	$94.15	$94.15	$94.20
Purchase #7	$130.55	12.282%	$146.5842	$146.58	$146.60	$146.60
7 purchase totals =	$990.58		$1,082.9044	$1,082.90	$1,082.95	$1,083.10