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	$241.70	6.124%	$256.5017	$256.50	$256.50	$256.50
Purchase #2	$138.86	7.177%	$148.826	$148.83	$148.85	$148.80
Purchase #3	$133.27	3.777%	$138.3036	$138.30	$138.30	$138.30
Purchase #4	$149.70	4.695%	$156.7284	$156.73	$156.75	$156.70
Purchase #5	$204.91	8.137%	$221.5835	$221.58	$221.60	$221.60
Purchase #6	$123.76	11.400%	$137.8686	$137.87	$137.85	$137.90
Purchase #7	$42.36	8.336%	$45.8911	$45.89	$45.90	$45.90
7 purchase totals =	$1,034.56		$1,105.7029	$1,105.70	$1,105.75	$1,105.70