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	$20.83	13.665%	$23.6764	$23.68	$23.70	$23.70
Purchase #2	$71.64	6.814%	$76.5215	$76.52	$76.50	$76.50
Purchase #3	$199.30	13.806%	$226.8154	$226.82	$226.80	$226.80
Purchase #4	$85.96	5.465%	$90.6577	$90.66	$90.65	$90.70
Purchase #5	$31.52	8.840%	$34.3064	$34.31	$34.30	$34.30
Purchase #6	$35.46	11.828%	$39.6542	$39.65	$39.65	$39.70
Purchase #7	$99.38	12.247%	$111.5511	$111.55	$111.55	$111.60
7 purchase totals =	$544.09		$603.1827	$603.19	$603.15	$603.30