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	$231.83	10.633%	$256.4805	$256.48	$256.50	$256.50
Purchase #2	$17.64	10.202%	$19.4396	$19.44	$19.45	$19.40
Purchase #3	$127.90	3.669%	$132.5927	$132.59	$132.60	$132.60
Purchase #4	$88.93	7.780%	$95.8488	$95.85	$95.85	$95.80
Purchase #5	$74.44	5.823%	$78.7746	$78.77	$78.75	$78.80
Purchase #6	$6.65	3.314%	$6.8704	$6.87	$6.85	$6.90
Purchase #7	$10.35	9.637%	$11.3474	$11.35	$11.35	$11.30
7 purchase totals =	$557.74		$601.3540	$601.35	$601.35	$601.30