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	$190.97	12.366%	$214.5854	$214.59	$214.60	$214.60
Purchase #2	$226.40	7.858%	$244.1905	$244.19	$244.20	$244.20
Purchase #3	$49.87	11.126%	$55.4185	$55.42	$55.40	$55.40
Purchase #4	$115.58	6.602%	$123.2106	$123.21	$123.20	$123.20
Purchase #5	$129.85	11.277%	$144.4932	$144.49	$144.50	$144.50
Purchase #6	$6.95	9.278%	$7.5948	$7.59	$7.60	$7.60
Purchase #7	$80.84	5.646%	$85.4042	$85.40	$85.40	$85.40
7 purchase totals =	$800.46		$874.8972	$874.89	$874.90	$874.90