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	$14.61	7.464%	$15.7005	$15.70	$15.70	$15.70
Purchase #2	$85.39	3.751%	$88.593	$88.59	$88.60	$88.60
Purchase #3	$40.47	5.359%	$42.6388	$42.64	$42.65	$42.60
Purchase #4	$138.54	10.217%	$152.6946	$152.69	$152.70	$152.70
Purchase #5	$61.86	10.716%	$68.4889	$68.49	$68.50	$68.50
Purchase #6	$231.57	10.587%	$256.0863	$256.09	$256.10	$256.10
Purchase #7	$11.38	10.549%	$12.5805	$12.58	$12.60	$12.60
7 purchase totals =	$583.82		$636.7826	$636.78	$636.85	$636.80