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	$5.85	10.793%	$6.4814	$6.48	$6.50	$6.50
Purchase #2	$224.44	13.870%	$255.5698	$255.57	$255.55	$255.60
Purchase #3	$161.99	13.196%	$183.3662	$183.37	$183.35	$183.40
Purchase #4	$52.89	11.722%	$59.0898	$59.09	$59.10	$59.10
Purchase #5	$90.93	12.651%	$102.4336	$102.43	$102.45	$102.40
Purchase #6	$101.52	5.647%	$107.2528	$107.25	$107.25	$107.30
Purchase #7	$181.89	8.123%	$196.6649	$196.66	$196.65	$196.70
7 purchase totals =	$819.51		$910.8585	$910.85	$910.85	$911.00