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	$156.99	5.138%	$165.0561	$165.06	$165.05	$165.10
Purchase #2	$63.83	3.617%	$66.1387	$66.14	$66.15	$66.10
Purchase #3	$209.30	12.230%	$234.8974	$234.90	$234.90	$234.90
Purchase #4	$222.86	4.715%	$233.3678	$233.37	$233.35	$233.40
Purchase #5	$18.66	9.226%	$20.3816	$20.38	$20.40	$20.40
Purchase #6	$117.92	8.430%	$127.8607	$127.86	$127.85	$127.90
Purchase #7	$100.86	3.386%	$104.2751	$104.28	$104.30	$104.30
7 purchase totals =	$890.42		$951.9774	$951.99	$952.00	$952.10