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	$99.83	6.103%	$105.9226	$105.92	$105.90	$105.90
Purchase #2	$40.58	9.509%	$44.4388	$44.44	$44.45	$44.40
Purchase #3	$213.80	7.823%	$230.5256	$230.53	$230.55	$230.50
Purchase #4	$139.38	3.268%	$143.9349	$143.93	$143.95	$143.90
Purchase #5	$18.95	10.632%	$20.9648	$20.96	$20.95	$21.00
Purchase #6	$80.38	10.851%	$89.102	$89.10	$89.10	$89.10
Purchase #7	$227.47	13.764%	$258.779	$258.78	$258.80	$258.80
7 purchase totals =	$820.39		$893.6677	$893.66	$893.70	$893.60