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	$18.49	11.296%	$20.5786	$20.58	$20.60	$20.60
Purchase #2	$30.46	3.248%	$31.4493	$31.45	$31.45	$31.40
Purchase #3	$99.60	4.622%	$104.2035	$104.20	$104.20	$104.20
Purchase #4	$99.63	11.408%	$110.9958	$111.00	$111.00	$111.00
Purchase #5	$47.86	8.508%	$51.9319	$51.93	$51.95	$51.90
Purchase #6	$92.65	8.829%	$100.8301	$100.83	$100.85	$100.80
Purchase #7	$82.90	11.641%	$92.5504	$92.55	$92.55	$92.60
7 purchase totals =	$471.59		$512.5396	$512.54	$512.60	$512.50