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	$116.77	13.165%	$132.1428	$132.14	$132.15	$132.10
Purchase #2	$49.64	10.612%	$54.9078	$54.91	$54.90	$54.90
Purchase #3	$82.25	8.208%	$89.0011	$89.00	$89.00	$89.00
Purchase #4	$96.56	9.348%	$105.5864	$105.59	$105.60	$105.60
Purchase #5	$113.71	11.698%	$127.0118	$127.01	$127.00	$127.00
Purchase #6	$229.50	10.202%	$252.9136	$252.91	$252.90	$252.90
Purchase #7	$159.53	8.713%	$173.4298	$173.43	$173.45	$173.40
7 purchase totals =	$847.96		$934.9933	$934.99	$935.00	$934.90