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	$192.57	6.763%	$205.5935	$205.59	$205.60	$205.60
Purchase #2	$168.49	10.613%	$186.3718	$186.37	$186.35	$186.40
Purchase #3	$166.27	11.801%	$185.8915	$185.89	$185.90	$185.90
Purchase #4	$208.66	7.291%	$223.8734	$223.87	$223.85	$223.90
Purchase #5	$245.54	11.652%	$274.1503	$274.15	$274.15	$274.20
Purchase #6	$225.37	10.195%	$248.3465	$248.35	$248.35	$248.30
Purchase #7	$13.91	12.174%	$15.6034	$15.60	$15.60	$15.60
7 purchase totals =	$1,220.81		$1,339.8304	$1,339.82	$1,339.80	$1,339.90