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	$55.70	12.778%	$62.8173	$62.82	$62.80	$62.80
Purchase #2	$75.65	4.254%	$78.8682	$78.87	$78.85	$78.90
Purchase #3	$244.50	6.554%	$260.5245	$260.52	$260.50	$260.50
Purchase #4	$61.80	9.343%	$67.574	$67.57	$67.55	$67.60
Purchase #5	$34.89	10.272%	$38.4739	$38.47	$38.45	$38.50
Purchase #6	$6.92	4.722%	$7.2468	$7.25	$7.25	$7.20
Purchase #7	$122.71	8.282%	$132.8728	$132.87	$132.85	$132.90
7 purchase totals =	$602.17		$648.3775	$648.37	$648.25	$648.40