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	$24.45	10.496%	$27.0163	$27.02	$27.00	$27.00
Purchase #2	$127.81	7.481%	$137.3715	$137.37	$137.35	$137.40
Purchase #3	$193.60	12.426%	$217.6567	$217.66	$217.65	$217.70
Purchase #4	$35.85	12.610%	$40.3707	$40.37	$40.35	$40.40
Purchase #5	$149.44	7.516%	$160.6719	$160.67	$160.65	$160.70
Purchase #6	$166.26	11.462%	$185.3167	$185.32	$185.30	$185.30
Purchase #7	$214.98	8.612%	$233.4941	$233.49	$233.50	$233.50
7 purchase totals =	$912.39		$1,001.8979	$1,001.90	$1,001.80	$1,002.00