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	$135.72	6.781%	$144.9232	$144.92	$144.90	$144.90
Purchase #2	$120.42	13.335%	$136.478	$136.48	$136.50	$136.50
Purchase #3	$19.48	13.151%	$22.0418	$22.04	$22.05	$22.00
Purchase #4	$145.64	3.492%	$150.7257	$150.73	$150.75	$150.70
Purchase #5	$94.32	11.855%	$105.5016	$105.50	$105.50	$105.50
Purchase #6	$19.66	7.613%	$21.1567	$21.16	$21.15	$21.20
Purchase #7	$53.25	10.155%	$58.6575	$58.66	$58.65	$58.70
7 purchase totals =	$588.49		$639.4845	$639.49	$639.50	$639.50