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	$37.85	11.687%	$42.2735	$42.27	$42.25	$42.30
Purchase #2	$212.30	13.114%	$240.141	$240.14	$240.15	$240.10
Purchase #3	$250.32	5.232%	$263.4167	$263.42	$263.40	$263.40
Purchase #4	$168.98	6.235%	$179.5159	$179.52	$179.50	$179.50
Purchase #5	$237.90	3.602%	$246.4692	$246.47	$246.45	$246.50
Purchase #6	$138.45	3.750%	$143.6419	$143.64	$143.65	$143.60
Purchase #7	$20.85	4.491%	$21.7864	$21.79	$21.80	$21.80
7 purchase totals =	$1,066.65		$1,137.2446	$1,137.25	$1,137.20	$1,137.20