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	$210.30	8.793%	$228.7917	$228.79	$228.80	$228.80
Purchase #2	$247.63	11.339%	$275.7088	$275.71	$275.70	$275.70
Purchase #3	$112.27	12.774%	$126.6114	$126.61	$126.60	$126.60
Purchase #4	$129.77	6.280%	$137.9196	$137.92	$137.90	$137.90
Purchase #5	$210.54	5.504%	$222.1281	$222.13	$222.15	$222.10
Purchase #6	$132.27	4.679%	$138.4589	$138.46	$138.45	$138.50
Purchase #7	$98.51	6.161%	$104.5792	$104.58	$104.60	$104.60
7 purchase totals =	$1,141.29		$1,234.1977	$1,234.20	$1,234.20	$1,234.20