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	$109.54	8.647%	$119.0119	$119.01	$119.00	$119.00
Purchase #2	$43.38	9.196%	$47.3692	$47.37	$47.35	$47.40
Purchase #3	$39.77	7.774%	$42.8617	$42.86	$42.85	$42.90
Purchase #4	$38.63	10.660%	$42.748	$42.75	$42.75	$42.70
Purchase #5	$239.46	11.158%	$266.1789	$266.18	$266.20	$266.20
Purchase #6	$10.80	9.146%	$11.7878	$11.79	$11.80	$11.80
Purchase #7	$131.57	5.694%	$139.0616	$139.06	$139.05	$139.10
7 purchase totals =	$613.15		$669.0191	$669.02	$669.00	$669.10