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	$81.70	10.176%	$90.0138	$90.01	$90.00	$90.00
Purchase #2	$208.26	10.696%	$230.5355	$230.54	$230.55	$230.50
Purchase #3	$170.73	11.692%	$190.6918	$190.69	$190.70	$190.70
Purchase #4	$239.99	10.606%	$265.4433	$265.44	$265.45	$265.40
Purchase #5	$74.45	10.778%	$82.4742	$82.47	$82.45	$82.50
Purchase #6	$10.68	9.181%	$11.6605	$11.66	$11.65	$11.70
Purchase #7	$212.64	4.710%	$222.6553	$222.66	$222.65	$222.70
7 purchase totals =	$998.45		$1,093.4744	$1,093.47	$1,093.45	$1,093.50