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	$247.67	3.250%	$255.7193	$255.72	$255.70	$255.70
Purchase #2	$20.46	6.293%	$21.7475	$21.75	$21.75	$21.70
Purchase #3	$35.40	10.433%	$39.0933	$39.09	$39.10	$39.10
Purchase #4	$162.44	5.352%	$171.1338	$171.13	$171.15	$171.10
Purchase #5	$117.29	13.279%	$132.8649	$132.86	$132.85	$132.90
Purchase #6	$102.83	4.778%	$107.7432	$107.74	$107.75	$107.70
Purchase #7	$228.64	11.831%	$255.6904	$255.69	$255.70	$255.70
7 purchase totals =	$914.73		$983.9924	$983.98	$984.00	$983.90