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	$51.72	13.382%	$58.6412	$58.64	$58.65	$58.60
Purchase #2	$152.76	12.257%	$171.4838	$171.48	$171.50	$171.50
Purchase #3	$158.70	9.174%	$173.2591	$173.26	$173.25	$173.30
Purchase #4	$121.35	11.246%	$134.997	$135.00	$135.00	$135.00
Purchase #5	$59.35	3.791%	$61.6	$61.60	$61.60	$61.60
Purchase #6	$75.38	10.232%	$83.0929	$83.09	$83.10	$83.10
Purchase #7	$95.72	3.845%	$99.4004	$99.40	$99.40	$99.40
7 purchase totals =	$714.98		$782.4744	$782.47	$782.50	$782.50