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	$247.50	7.293%	$265.5502	$265.55	$265.55	$265.60
Purchase #2	$250.48	12.117%	$280.8307	$280.83	$280.85	$280.80
Purchase #3	$212.97	13.627%	$241.9914	$241.99	$242.00	$242.00
Purchase #4	$177.65	10.587%	$196.4578	$196.46	$196.45	$196.50
Purchase #5	$80.39	12.795%	$90.6759	$90.68	$90.70	$90.70
Purchase #6	$14.71	4.408%	$15.3584	$15.36	$15.35	$15.40
Purchase #7	$63.82	12.588%	$71.8537	$71.85	$71.85	$71.90
7 purchase totals =	$1,047.52		$1,162.7181	$1,162.72	$1,162.75	$1,162.90