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	$191.32	13.608%	$217.3548	$217.35	$217.35	$217.40
Purchase #2	$134.27	10.226%	$148.0005	$148.00	$148.00	$148.00
Purchase #3	$63.66	4.302%	$66.3987	$66.40	$66.40	$66.40
Purchase #4	$10.34	10.199%	$11.3946	$11.39	$11.40	$11.40
Purchase #5	$40.27	4.873%	$42.2324	$42.23	$42.25	$42.20
Purchase #6	$240.67	7.436%	$258.5662	$258.57	$258.55	$258.60
Purchase #7	$81.60	11.355%	$90.8657	$90.87	$90.85	$90.90
7 purchase totals =	$762.13		$834.8129	$834.81	$834.80	$834.90