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	$38.84	11.265%	$43.2153	$43.22	$43.20	$43.20
Purchase #2	$31.90	8.176%	$34.5081	$34.51	$34.50	$34.50
Purchase #3	$247.42	3.243%	$255.4438	$255.44	$255.45	$255.40
Purchase #4	$93.43	11.647%	$104.3118	$104.31	$104.30	$104.30
Purchase #5	$13.87	10.838%	$15.3732	$15.37	$15.35	$15.40
Purchase #6	$198.85	7.558%	$213.8791	$213.88	$213.90	$213.90
Purchase #7	$19.99	9.615%	$21.912	$21.91	$21.90	$21.90
7 purchase totals =	$644.30		$688.6433	$688.64	$688.60	$688.60