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	$24.84	8.761%	$27.0162	$27.02	$27.00	$27.00
Purchase #2	$142.87	7.848%	$154.0824	$154.08	$154.10	$154.10
Purchase #3	$121.46	5.245%	$127.8306	$127.83	$127.85	$127.80
Purchase #4	$30.35	4.687%	$31.7725	$31.77	$31.75	$31.80
Purchase #5	$162.90	11.491%	$181.6188	$181.62	$181.60	$181.60
Purchase #6	$172.45	12.328%	$193.7096	$193.71	$193.70	$193.70
Purchase #7	$180.71	8.798%	$196.6089	$196.61	$196.60	$196.60
7 purchase totals =	$835.58		$912.6390	$912.64	$912.60	$912.60