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	$28.27	11.863%	$31.6237	$31.62	$31.60	$31.60
Purchase #2	$192.35	12.161%	$215.7417	$215.74	$215.75	$215.70
Purchase #3	$85.87	4.335%	$89.5925	$89.59	$89.60	$89.60
Purchase #4	$29.85	5.344%	$31.4452	$31.45	$31.45	$31.40
Purchase #5	$186.88	5.273%	$196.7342	$196.73	$196.75	$196.70
Purchase #6	$184.86	10.512%	$204.2925	$204.29	$204.30	$204.30
Purchase #7	$154.61	12.174%	$173.4322	$173.43	$173.45	$173.40
7 purchase totals =	$862.69		$942.8620	$942.85	$942.90	$942.70