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	$150.68	6.229%	$160.0659	$160.07	$160.05	$160.10
Purchase #2	$111.85	12.873%	$126.2485	$126.25	$126.25	$126.20
Purchase #3	$114.32	8.410%	$123.9343	$123.93	$123.95	$123.90
Purchase #4	$214.45	5.321%	$225.8609	$225.86	$225.85	$225.90
Purchase #5	$61.27	10.334%	$67.6016	$67.60	$67.60	$67.60
Purchase #6	$132.48	13.465%	$150.3184	$150.32	$150.30	$150.30
Purchase #7	$20.93	11.644%	$23.3671	$23.37	$23.35	$23.40
7 purchase totals =	$805.98		$877.3967	$877.40	$877.35	$877.40