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	$81.80	10.826%	$90.6557	$90.66	$90.65	$90.70
Purchase #2	$237.87	4.316%	$248.1365	$248.14	$248.15	$248.10
Purchase #3	$66.40	9.287%	$72.5666	$72.57	$72.55	$72.60
Purchase #4	$36.58	10.188%	$40.3068	$40.31	$40.30	$40.30
Purchase #5	$178.87	8.709%	$194.4478	$194.45	$194.45	$194.40
Purchase #6	$84.34	13.265%	$95.5277	$95.53	$95.55	$95.50
Purchase #7	$41.61	5.682%	$43.9743	$43.97	$43.95	$44.00
7 purchase totals =	$727.47		$785.6154	$785.63	$785.60	$785.60