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	$159.86	6.294%	$169.9216	$169.92	$169.90	$169.90
Purchase #2	$52.31	6.303%	$55.6071	$55.61	$55.60	$55.60
Purchase #3	$86.53	9.658%	$94.8871	$94.89	$94.90	$94.90
Purchase #4	$124.99	5.465%	$131.8207	$131.82	$131.80	$131.80
Purchase #5	$20.96	12.293%	$23.5366	$23.54	$23.55	$23.50
Purchase #6	$40.69	13.396%	$46.1408	$46.14	$46.15	$46.10
Purchase #7	$12.55	3.720%	$13.0169	$13.02	$13.00	$13.00
7 purchase totals =	$497.89		$534.9308	$534.94	$534.90	$534.80