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	$127.42	12.779%	$143.703	$143.70	$143.70	$143.70
Purchase #2	$214.71	3.603%	$222.446	$222.45	$222.45	$222.40
Purchase #3	$58.35	7.718%	$62.8535	$62.85	$62.85	$62.90
Purchase #4	$45.78	6.243%	$48.638	$48.64	$48.65	$48.60
Purchase #5	$229.82	4.663%	$240.5365	$240.54	$240.55	$240.50
Purchase #6	$29.86	4.324%	$31.1511	$31.15	$31.15	$31.20
Purchase #7	$132.96	6.420%	$141.496	$141.50	$141.50	$141.50
7 purchase totals =	$838.90		$890.8241	$890.83	$890.85	$890.80