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	$112.35	13.734%	$127.7801	$127.78	$127.80	$127.80
Purchase #2	$68.64	10.586%	$75.9062	$75.91	$75.90	$75.90
Purchase #3	$184.59	5.455%	$194.6594	$194.66	$194.65	$194.70
Purchase #4	$38.34	3.142%	$39.5446	$39.54	$39.55	$39.50
Purchase #5	$89.79	10.491%	$99.2099	$99.21	$99.20	$99.20
Purchase #6	$231.49	10.818%	$256.5326	$256.53	$256.55	$256.50
Purchase #7	$37.92	8.863%	$41.2808	$41.28	$41.30	$41.30
7 purchase totals =	$763.12		$834.9136	$834.91	$834.95	$834.90