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	$19.88	8.561%	$21.5819	$21.58	$21.60	$21.60
Purchase #2	$107.83	6.631%	$114.9802	$114.98	$115.00	$115.00
Purchase #3	$78.67	8.569%	$85.4112	$85.41	$85.40	$85.40
Purchase #4	$214.45	6.603%	$228.6101	$228.61	$228.60	$228.60
Purchase #5	$90.77	13.533%	$103.0539	$103.05	$103.05	$103.10
Purchase #6	$122.90	13.605%	$139.6205	$139.62	$139.60	$139.60
Purchase #7	$168.42	10.745%	$186.5167	$186.52	$186.50	$186.50
7 purchase totals =	$802.92		$879.7745	$879.77	$879.75	$879.80