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	$111.87	8.598%	$121.4886	$121.49	$121.50	$121.50
Purchase #2	$72.62	10.246%	$80.0606	$80.06	$80.05	$80.10
Purchase #3	$102.73	13.841%	$116.9489	$116.95	$116.95	$116.90
Purchase #4	$217.77	7.168%	$233.3798	$233.38	$233.40	$233.40
Purchase #5	$112.57	13.576%	$127.8525	$127.85	$127.85	$127.90
Purchase #6	$85.99	11.719%	$96.0672	$96.07	$96.05	$96.10
Purchase #7	$97.28	11.685%	$108.6472	$108.65	$108.65	$108.60
7 purchase totals =	$800.83		$884.4448	$884.45	$884.45	$884.50