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	$131.31	11.606%	$146.5498	$146.55	$146.55	$146.50
Purchase #2	$72.59	13.432%	$82.3403	$82.34	$82.35	$82.30
Purchase #3	$44.26	8.174%	$47.8778	$47.88	$47.90	$47.90
Purchase #4	$62.89	8.105%	$67.9872	$67.99	$68.00	$68.00
Purchase #5	$105.65	11.189%	$117.4712	$117.47	$117.45	$117.50
Purchase #6	$99.50	3.552%	$103.0342	$103.03	$103.05	$103.00
Purchase #7	$12.57	8.464%	$13.6339	$13.63	$13.65	$13.60
7 purchase totals =	$528.77		$578.8944	$578.89	$578.95	$578.80