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	$95.45	4.636%	$99.8751	$99.88	$99.90	$99.90
Purchase #2	$201.62	12.206%	$226.2297	$226.23	$226.25	$226.20
Purchase #3	$122.34	8.122%	$132.2765	$132.28	$132.30	$132.30
Purchase #4	$220.99	5.777%	$233.7566	$233.76	$233.75	$233.80
Purchase #5	$66.52	9.290%	$72.6997	$72.70	$72.70	$72.70
Purchase #6	$242.96	6.227%	$258.0891	$258.09	$258.10	$258.10
Purchase #7	$105.85	10.424%	$116.8838	$116.88	$116.90	$116.90
7 purchase totals =	$1,055.73		$1,139.8105	$1,139.82	$1,139.90	$1,139.90