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	$62.91	6.152%	$66.7802	$66.78	$66.80	$66.80
Purchase #2	$212.84	13.641%	$241.8735	$241.87	$241.85	$241.90
Purchase #3	$215.64	3.127%	$222.3831	$222.38	$222.40	$222.40
Purchase #4	$176.86	11.387%	$196.999	$197.00	$197.00	$197.00
Purchase #5	$74.66	4.826%	$78.2631	$78.26	$78.25	$78.30
Purchase #6	$68.38	10.452%	$75.5271	$75.53	$75.55	$75.50
Purchase #7	$54.98	3.793%	$57.0654	$57.07	$57.05	$57.10
7 purchase totals =	$866.27		$938.8914	$938.89	$938.90	$939.00