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	$143.66	3.418%	$148.5703	$148.57	$148.55	$148.60
Purchase #2	$209.36	3.686%	$217.077	$217.08	$217.10	$217.10
Purchase #3	$32.76	8.575%	$35.5692	$35.57	$35.55	$35.60
Purchase #4	$44.27	4.377%	$46.2077	$46.21	$46.20	$46.20
Purchase #5	$20.94	4.242%	$21.8283	$21.83	$21.85	$21.80
Purchase #6	$60.55	5.393%	$63.8155	$63.82	$63.80	$63.80
Purchase #7	$127.56	3.335%	$131.8141	$131.81	$131.80	$131.80
7 purchase totals =	$639.10		$664.8821	$664.89	$664.85	$664.90