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	$42.46	11.123%	$47.1828	$47.18	$47.20	$47.20
Purchase #2	$146.45	12.508%	$164.768	$164.77	$164.75	$164.80
Purchase #3	$131.69	6.149%	$139.7876	$139.79	$139.80	$139.80
Purchase #4	$10.74	6.782%	$11.4684	$11.47	$11.45	$11.50
Purchase #5	$63.34	12.789%	$71.4406	$71.44	$71.45	$71.40
Purchase #6	$29.71	4.637%	$31.0877	$31.09	$31.10	$31.10
Purchase #7	$48.52	6.228%	$51.5418	$51.54	$51.55	$51.50
7 purchase totals =	$472.91		$517.2769	$517.28	$517.30	$517.30