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	$132.27	8.852%	$143.9785	$143.98	$144.00	$144.00
Purchase #2	$156.47	11.411%	$174.3248	$174.32	$174.30	$174.30
Purchase #3	$53.96	5.312%	$56.8264	$56.83	$56.85	$56.80
Purchase #4	$12.79	9.549%	$14.0113	$14.01	$14.00	$14.00
Purchase #5	$104.65	6.328%	$111.2723	$111.27	$111.25	$111.30
Purchase #6	$217.28	3.845%	$225.6344	$225.63	$225.65	$225.60
Purchase #7	$102.64	3.717%	$106.4551	$106.46	$106.45	$106.50
7 purchase totals =	$780.06		$832.5028	$832.50	$832.50	$832.50