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	$120.57	10.247%	$132.9248	$132.92	$132.90	$132.90
Purchase #2	$104.27	13.653%	$118.506	$118.51	$118.50	$118.50
Purchase #3	$161.87	11.392%	$180.3102	$180.31	$180.30	$180.30
Purchase #4	$139.26	3.154%	$143.6523	$143.65	$143.65	$143.70
Purchase #5	$101.60	9.304%	$111.0529	$111.05	$111.05	$111.10
Purchase #6	$58.31	11.151%	$64.8121	$64.81	$64.80	$64.80
Purchase #7	$95.94	8.293%	$103.8963	$103.90	$103.90	$103.90
7 purchase totals =	$781.82		$855.1546	$855.15	$855.10	$855.20