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	$5.80	10.622%	$6.4161	$6.42	$6.40	$6.40
Purchase #2	$91.75	9.666%	$100.6186	$100.62	$100.60	$100.60
Purchase #3	$194.64	9.169%	$212.4865	$212.49	$212.50	$212.50
Purchase #4	$44.79	3.437%	$46.3294	$46.33	$46.35	$46.30
Purchase #5	$240.89	3.153%	$248.4853	$248.49	$248.50	$248.50
Purchase #6	$231.52	13.336%	$262.3955	$262.40	$262.40	$262.40
Purchase #7	$50.92	6.768%	$54.3663	$54.37	$54.35	$54.40
7 purchase totals =	$860.31		$931.0977	$931.12	$931.10	$931.10