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	$25.48	5.380%	$26.8508	$26.85	$26.85	$26.90
Purchase #2	$163.43	5.559%	$172.5151	$172.52	$172.50	$172.50
Purchase #3	$93.78	10.329%	$103.4665	$103.47	$103.45	$103.50
Purchase #4	$198.84	8.200%	$215.1449	$215.14	$215.15	$215.10
Purchase #5	$99.44	12.128%	$111.5001	$111.50	$111.50	$111.50
Purchase #6	$175.35	13.870%	$199.671	$199.67	$199.65	$199.70
Purchase #7	$93.90	8.538%	$101.9172	$101.92	$101.90	$101.90
7 purchase totals =	$850.22		$931.0656	$931.07	$931.00	$931.10