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	$80.78	4.572%	$84.4733	$84.47	$84.45	$84.50
Purchase #2	$213.68	4.159%	$222.567	$222.57	$222.55	$222.60
Purchase #3	$126.64	11.219%	$140.8477	$140.85	$140.85	$140.80
Purchase #4	$47.86	12.461%	$53.8238	$53.82	$53.80	$53.80
Purchase #5	$95.87	5.174%	$100.8303	$100.83	$100.85	$100.80
Purchase #6	$103.72	12.784%	$116.9796	$116.98	$117.00	$117.00
Purchase #7	$220.33	9.598%	$241.4773	$241.48	$241.50	$241.50
7 purchase totals =	$888.88		$960.9990	$961.00	$961.00	$961.00