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	$7.85	7.601%	$8.4467	$8.45	$8.45	$8.40
Purchase #2	$140.59	8.131%	$152.0214	$152.02	$152.00	$152.00
Purchase #3	$103.49	7.351%	$111.0975	$111.10	$111.10	$111.10
Purchase #4	$91.27	13.337%	$103.4427	$103.44	$103.45	$103.40
Purchase #5	$58.72	6.422%	$62.491	$62.49	$62.50	$62.50
Purchase #6	$60.53	4.685%	$63.3658	$63.37	$63.35	$63.40
Purchase #7	$209.99	8.554%	$227.9525	$227.95	$227.95	$228.00
7 purchase totals =	$672.44		$728.8176	$728.82	$728.80	$728.80