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	$42.85	10.645%	$47.4114	$47.41	$47.40	$47.40
Purchase #2	$30.45	8.860%	$33.1479	$33.15	$33.15	$33.10
Purchase #3	$141.32	9.410%	$154.6182	$154.62	$154.60	$154.60
Purchase #4	$94.45	10.600%	$104.4617	$104.46	$104.45	$104.50
Purchase #5	$134.60	6.610%	$143.4971	$143.50	$143.50	$143.50
Purchase #6	$124.40	10.809%	$137.8464	$137.85	$137.85	$137.80
Purchase #7	$117.64	8.728%	$127.9076	$127.91	$127.90	$127.90
7 purchase totals =	$685.71		$748.8903	$748.90	$748.85	$748.80