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	$143.92	8.756%	$156.5216	$156.52	$156.50	$156.50
Purchase #2	$162.61	12.429%	$182.8208	$182.82	$182.80	$182.80
Purchase #3	$233.90	10.610%	$258.7168	$258.72	$258.70	$258.70
Purchase #4	$102.51	6.721%	$109.3997	$109.40	$109.40	$109.40
Purchase #5	$51.35	10.748%	$56.8691	$56.87	$56.85	$56.90
Purchase #6	$47.47	10.376%	$52.3955	$52.40	$52.40	$52.40
Purchase #7	$47.38	3.259%	$48.9241	$48.92	$48.90	$48.90
7 purchase totals =	$789.14		$865.6476	$865.65	$865.55	$865.60