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	$24.98	8.842%	$27.1887	$27.19	$27.20	$27.20
Purchase #2	$196.46	13.161%	$222.3161	$222.32	$222.30	$222.30
Purchase #3	$69.26	4.780%	$72.5706	$72.57	$72.55	$72.60
Purchase #4	$161.66	11.252%	$179.85	$179.85	$179.85	$179.90
Purchase #5	$196.26	9.386%	$214.681	$214.68	$214.70	$214.70
Purchase #6	$230.90	10.606%	$255.3893	$255.39	$255.40	$255.40
Purchase #7	$54.39	12.548%	$61.2149	$61.21	$61.20	$61.20
7 purchase totals =	$933.91		$1,033.2106	$1,033.21	$1,033.20	$1,033.30