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	$33.71	12.684%	$37.9858	$37.99	$38.00	$38.00
Purchase #2	$240.32	6.383%	$255.6596	$255.66	$255.65	$255.70
Purchase #3	$166.42	3.200%	$171.7454	$171.75	$171.75	$171.70
Purchase #4	$141.48	3.738%	$146.7685	$146.77	$146.75	$146.80
Purchase #5	$54.67	4.440%	$57.0973	$57.10	$57.10	$57.10
Purchase #6	$204.37	8.861%	$222.4792	$222.48	$222.50	$222.50
Purchase #7	$238.27	4.708%	$249.4878	$249.49	$249.50	$249.50
7 purchase totals =	$1,079.24		$1,141.2236	$1,141.24	$1,141.25	$1,141.30