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	$249.46	3.676%	$258.6301	$258.63	$258.65	$258.60
Purchase #2	$19.89	8.685%	$21.6174	$21.62	$21.60	$21.60
Purchase #3	$33.87	7.332%	$36.3533	$36.35	$36.35	$36.40
Purchase #4	$44.56	11.553%	$49.708	$49.71	$49.70	$49.70
Purchase #5	$33.37	5.638%	$35.2514	$35.25	$35.25	$35.30
Purchase #6	$70.94	10.613%	$78.4689	$78.47	$78.45	$78.50
Purchase #7	$161.80	10.258%	$178.3974	$178.40	$178.40	$178.40
7 purchase totals =	$613.89		$658.4265	$658.43	$658.40	$658.50