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	$217.90	9.294%	$238.1516	$238.15	$238.15	$238.20
Purchase #2	$150.60	4.801%	$157.8303	$157.83	$157.85	$157.80
Purchase #3	$232.77	5.126%	$244.7018	$244.70	$244.70	$244.70
Purchase #4	$18.92	10.321%	$20.8727	$20.87	$20.85	$20.90
Purchase #5	$30.47	6.542%	$32.4633	$32.46	$32.45	$32.50
Purchase #6	$90.40	11.148%	$100.4778	$100.48	$100.50	$100.50
Purchase #7	$231.90	5.510%	$244.6777	$244.68	$244.70	$244.70
7 purchase totals =	$972.96		$1,039.1752	$1,039.17	$1,039.20	$1,039.30