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	$82.54	8.361%	$89.4412	$89.44	$89.45	$89.40
Purchase #2	$212.89	13.432%	$241.4854	$241.49	$241.50	$241.50
Purchase #3	$18.79	9.200%	$20.5187	$20.52	$20.50	$20.50
Purchase #4	$154.86	12.451%	$174.1416	$174.14	$174.15	$174.10
Purchase #5	$233.60	3.807%	$242.4932	$242.49	$242.50	$242.50
Purchase #6	$10.61	4.474%	$11.0847	$11.08	$11.10	$11.10
Purchase #7	$74.72	13.554%	$84.8475	$84.85	$84.85	$84.80
7 purchase totals =	$788.01		$864.0123	$864.01	$864.05	$863.90