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	$51.35	3.730%	$53.2654	$53.27	$53.25	$53.30
Purchase #2	$86.58	3.551%	$89.6545	$89.65	$89.65	$89.70
Purchase #3	$30.78	10.842%	$34.1172	$34.12	$34.10	$34.10
Purchase #4	$150.32	6.436%	$159.9946	$159.99	$160.00	$160.00
Purchase #5	$105.35	13.536%	$119.6102	$119.61	$119.60	$119.60
Purchase #6	$95.90	8.103%	$103.6708	$103.67	$103.65	$103.70
Purchase #7	$200.94	12.690%	$226.4393	$226.44	$226.45	$226.40
7 purchase totals =	$721.22		$786.7520	$786.75	$786.70	$786.80