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	$241.97	12.535%	$272.3009	$272.30	$272.30	$272.30
Purchase #2	$74.48	10.227%	$82.0971	$82.10	$82.10	$82.10
Purchase #3	$117.83	4.618%	$123.2714	$123.27	$123.25	$123.30
Purchase #4	$143.53	10.210%	$158.1844	$158.18	$158.20	$158.20
Purchase #5	$236.90	8.712%	$257.5387	$257.54	$257.55	$257.50
Purchase #6	$172.89	3.684%	$179.2593	$179.26	$179.25	$179.30
Purchase #7	$12.63	7.418%	$13.5669	$13.57	$13.55	$13.60
7 purchase totals =	$1,000.23		$1,086.2187	$1,086.22	$1,086.20	$1,086.30