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	$239.98	4.803%	$251.5062	$251.51	$251.50	$251.50
Purchase #2	$81.86	13.160%	$92.6328	$92.63	$92.65	$92.60
Purchase #3	$60.64	4.170%	$63.1687	$63.17	$63.15	$63.20
Purchase #4	$132.94	11.709%	$148.5059	$148.51	$148.50	$148.50
Purchase #5	$245.68	13.473%	$278.7805	$278.78	$278.80	$278.80
Purchase #6	$42.41	7.342%	$45.5237	$45.52	$45.50	$45.50
Purchase #7	$195.91	10.622%	$216.7196	$216.72	$216.70	$216.70
7 purchase totals =	$999.42		$1,096.8374	$1,096.84	$1,096.80	$1,096.80