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	$247.75	13.305%	$280.7131	$280.71	$280.70	$280.70
Purchase #2	$83.77	13.702%	$95.2482	$95.25	$95.25	$95.20
Purchase #3	$95.82	3.245%	$98.9294	$98.93	$98.95	$98.90
Purchase #4	$184.81	6.199%	$196.2664	$196.27	$196.25	$196.30
Purchase #5	$12.82	8.197%	$13.8709	$13.87	$13.85	$13.90
Purchase #6	$46.96	5.534%	$49.5588	$49.56	$49.55	$49.60
Purchase #7	$116.60	10.105%	$128.3824	$128.38	$128.40	$128.40
7 purchase totals =	$788.53		$862.9692	$862.97	$862.95	$863.00