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	$17.49	6.688%	$18.6597	$18.66	$18.65	$18.70
Purchase #2	$153.72	9.492%	$168.3111	$168.31	$168.30	$168.30
Purchase #3	$31.60	7.607%	$34.0038	$34.00	$34.00	$34.00
Purchase #4	$152.86	13.230%	$173.0834	$173.08	$173.10	$173.10
Purchase #5	$101.28	8.429%	$109.8169	$109.82	$109.80	$109.80
Purchase #6	$108.72	10.153%	$119.7583	$119.76	$119.75	$119.80
Purchase #7	$88.82	6.736%	$94.8029	$94.80	$94.80	$94.80
7 purchase totals =	$654.49		$718.4361	$718.43	$718.40	$718.50