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	$97.84	11.682%	$109.2697	$109.27	$109.25	$109.30
Purchase #2	$28.56	10.219%	$31.4785	$31.48	$31.50	$31.50
Purchase #3	$16.35	13.241%	$18.5149	$18.51	$18.50	$18.50
Purchase #4	$18.71	12.609%	$21.0691	$21.07	$21.05	$21.10
Purchase #5	$192.81	8.333%	$208.8769	$208.88	$208.90	$208.90
Purchase #6	$29.35	7.379%	$31.5157	$31.52	$31.50	$31.50
Purchase #7	$221.71	8.789%	$241.1961	$241.20	$241.20	$241.20
7 purchase totals =	$605.33		$661.9209	$661.93	$661.90	$662.00