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	$84.90	10.385%	$93.7169	$93.72	$93.70	$93.70
Purchase #2	$241.59	6.307%	$256.8271	$256.83	$256.85	$256.80
Purchase #3	$52.89	9.280%	$57.7982	$57.80	$57.80	$57.80
Purchase #4	$75.59	12.565%	$85.0879	$85.09	$85.10	$85.10
Purchase #5	$95.62	10.264%	$105.4344	$105.43	$105.45	$105.40
Purchase #6	$89.70	10.228%	$98.8745	$98.87	$98.85	$98.90
Purchase #7	$117.88	5.197%	$124.0062	$124.01	$124.00	$124.00
7 purchase totals =	$758.17		$821.7452	$821.75	$821.75	$821.70