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	$162.46	5.259%	$171.0038	$171.00	$171.00	$171.00
Purchase #2	$19.60	5.105%	$20.6006	$20.60	$20.60	$20.60
Purchase #3	$184.45	10.686%	$204.1603	$204.16	$204.15	$204.20
Purchase #4	$17.73	10.175%	$19.534	$19.53	$19.55	$19.50
Purchase #5	$38.87	8.511%	$42.1782	$42.18	$42.20	$42.20
Purchase #6	$88.65	9.712%	$97.2597	$97.26	$97.25	$97.30
Purchase #7	$83.31	8.147%	$90.0973	$90.10	$90.10	$90.10
7 purchase totals =	$595.07		$644.8339	$644.83	$644.85	$644.90