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	$202.92	6.195%	$215.4909	$215.49	$215.50	$215.50
Purchase #2	$193.83	11.124%	$215.3916	$215.39	$215.40	$215.40
Purchase #3	$208.41	7.182%	$223.378	$223.38	$223.40	$223.40
Purchase #4	$109.34	6.506%	$116.4537	$116.45	$116.45	$116.50
Purchase #5	$44.87	11.308%	$49.9439	$49.94	$49.95	$49.90
Purchase #6	$29.70	10.667%	$32.8681	$32.87	$32.85	$32.90
Purchase #7	$217.54	9.149%	$237.4427	$237.44	$237.45	$237.40
7 purchase totals =	$1,006.61		$1,090.9689	$1,090.96	$1,091.00	$1,091.00