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	$129.33	7.744%	$139.3453	$139.35	$139.35	$139.30
Purchase #2	$68.39	10.827%	$75.7946	$75.79	$75.80	$75.80
Purchase #3	$180.52	8.730%	$196.2794	$196.28	$196.30	$196.30
Purchase #4	$94.59	11.294%	$105.273	$105.27	$105.25	$105.30
Purchase #5	$122.62	9.748%	$134.573	$134.57	$134.55	$134.60
Purchase #6	$83.83	7.203%	$89.8683	$89.87	$89.85	$89.90
Purchase #7	$222.50	4.127%	$231.6826	$231.68	$231.70	$231.70
7 purchase totals =	$901.78		$972.8162	$972.81	$972.80	$972.90