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	$16.89	9.754%	$18.5375	$18.54	$18.55	$18.50
Purchase #2	$146.30	5.687%	$154.6201	$154.62	$154.60	$154.60
Purchase #3	$88.64	12.633%	$99.8379	$99.84	$99.85	$99.80
Purchase #4	$229.96	12.665%	$259.0844	$259.08	$259.10	$259.10
Purchase #5	$227.59	12.693%	$256.478	$256.48	$256.50	$256.50
Purchase #6	$86.87	10.242%	$95.7672	$95.77	$95.75	$95.80
Purchase #7	$89.47	8.770%	$97.3165	$97.32	$97.30	$97.30
7 purchase totals =	$885.72		$981.6416	$981.65	$981.65	$981.60