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	$34.90	10.861%	$38.6905	$38.69	$38.70	$38.70
Purchase #2	$113.83	11.318%	$126.7133	$126.71	$126.70	$126.70
Purchase #3	$31.42	4.131%	$32.718	$32.72	$32.70	$32.70
Purchase #4	$239.76	7.167%	$256.9436	$256.94	$256.95	$256.90
Purchase #5	$174.92	4.310%	$182.4591	$182.46	$182.45	$182.50
Purchase #6	$136.30	6.451%	$145.0927	$145.09	$145.10	$145.10
Purchase #7	$18.83	11.538%	$21.0026	$21.00	$21.00	$21.00
7 purchase totals =	$749.96		$803.6198	$803.61	$803.60	$803.60