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	$215.86	12.179%	$242.1496	$242.15	$242.15	$242.10
Purchase #2	$127.57	12.478%	$143.4882	$143.49	$143.50	$143.50
Purchase #3	$92.78	3.374%	$95.9104	$95.91	$95.90	$95.90
Purchase #4	$68.96	9.528%	$75.5305	$75.53	$75.55	$75.50
Purchase #5	$241.45	6.850%	$257.9893	$257.99	$258.00	$258.00
Purchase #6	$212.64	4.603%	$222.4278	$222.43	$222.45	$222.40
Purchase #7	$31.31	13.124%	$35.4191	$35.42	$35.40	$35.40
7 purchase totals =	$990.57		$1,072.9149	$1,072.92	$1,072.95	$1,072.80