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	$135.78	5.581%	$143.3579	$143.36	$143.35	$143.40
Purchase #2	$224.71	7.458%	$241.4689	$241.47	$241.45	$241.50
Purchase #3	$116.83	6.172%	$124.0407	$124.04	$124.05	$124.00
Purchase #4	$53.85	7.310%	$57.7864	$57.79	$57.80	$57.80
Purchase #5	$233.30	12.559%	$262.6001	$262.60	$262.60	$262.60
Purchase #6	$77.28	10.755%	$85.5915	$85.59	$85.60	$85.60
Purchase #7	$43.25	7.625%	$46.5478	$46.55	$46.55	$46.50
7 purchase totals =	$885.00		$961.3933	$961.40	$961.40	$961.40