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	$249.32	5.441%	$262.8855	$262.89	$262.90	$262.90
Purchase #2	$114.51	13.434%	$129.8933	$129.89	$129.90	$129.90
Purchase #3	$247.42	6.863%	$264.4004	$264.40	$264.40	$264.40
Purchase #4	$31.61	9.217%	$34.5235	$34.52	$34.50	$34.50
Purchase #5	$208.61	6.759%	$222.7099	$222.71	$222.70	$222.70
Purchase #6	$217.89	7.189%	$233.5541	$233.55	$233.55	$233.60
Purchase #7	$237.89	8.436%	$257.9584	$257.96	$257.95	$258.00
7 purchase totals =	$1,307.25		$1,405.9251	$1,405.92	$1,405.90	$1,406.00