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	$132.64	8.792%	$144.3017	$144.30	$144.30	$144.30
Purchase #2	$79.56	5.194%	$83.6923	$83.69	$83.70	$83.70
Purchase #3	$58.69	13.382%	$66.5439	$66.54	$66.55	$66.50
Purchase #4	$45.84	12.318%	$51.4866	$51.49	$51.50	$51.50
Purchase #5	$154.91	10.455%	$171.1058	$171.11	$171.10	$171.10
Purchase #6	$34.57	3.341%	$35.725	$35.73	$35.75	$35.70
Purchase #7	$111.94	13.489%	$127.0396	$127.04	$127.05	$127.00
7 purchase totals =	$618.15		$679.8949	$679.90	$679.95	$679.80