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	$234.81	13.848%	$267.3265	$267.33	$267.35	$267.30
Purchase #2	$231.70	4.797%	$242.8146	$242.81	$242.80	$242.80
Purchase #3	$69.98	12.492%	$78.7219	$78.72	$78.70	$78.70
Purchase #4	$60.41	5.645%	$63.8201	$63.82	$63.80	$63.80
Purchase #5	$47.80	6.469%	$50.8922	$50.89	$50.90	$50.90
Purchase #6	$81.62	10.219%	$89.9607	$89.96	$89.95	$90.00
Purchase #7	$176.33	8.240%	$190.8596	$190.86	$190.85	$190.90
7 purchase totals =	$902.65		$984.3956	$984.39	$984.35	$984.40