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	$128.91	9.667%	$141.3717	$141.37	$141.35	$141.40
Purchase #2	$83.78	7.554%	$90.1087	$90.11	$90.10	$90.10
Purchase #3	$232.99	6.834%	$248.9125	$248.91	$248.90	$248.90
Purchase #4	$78.87	8.115%	$85.2703	$85.27	$85.25	$85.30
Purchase #5	$131.87	7.724%	$142.0556	$142.06	$142.05	$142.10
Purchase #6	$13.42	13.325%	$15.2082	$15.21	$15.20	$15.20
Purchase #7	$138.78	8.547%	$150.6415	$150.64	$150.65	$150.60
7 purchase totals =	$808.62		$873.5685	$873.57	$873.50	$873.60