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	$18.98	6.249%	$20.1661	$20.17	$20.15	$20.20
Purchase #2	$46.88	9.406%	$51.2895	$51.29	$51.30	$51.30
Purchase #3	$143.81	4.337%	$150.047	$150.05	$150.05	$150.00
Purchase #4	$12.94	6.844%	$13.8256	$13.83	$13.85	$13.80
Purchase #5	$214.84	5.630%	$226.9355	$226.94	$226.95	$226.90
Purchase #6	$36.79	3.395%	$38.039	$38.04	$38.05	$38.00
Purchase #7	$63.98	13.743%	$72.7728	$72.77	$72.75	$72.80
7 purchase totals =	$538.22		$573.0755	$573.09	$573.10	$573.00