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	$103.82	10.493%	$114.7138	$114.71	$114.70	$114.70
Purchase #2	$57.39	4.314%	$59.8658	$59.87	$59.85	$59.90
Purchase #3	$57.51	11.791%	$64.291	$64.29	$64.30	$64.30
Purchase #4	$124.52	8.447%	$135.0382	$135.04	$135.05	$135.00
Purchase #5	$119.72	3.117%	$123.4517	$123.45	$123.45	$123.50
Purchase #6	$64.54	6.317%	$68.617	$68.62	$68.60	$68.60
Purchase #7	$97.86	3.198%	$100.9896	$100.99	$101.00	$101.00
7 purchase totals =	$625.36		$666.9671	$666.97	$666.95	$667.00