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	$37.78	6.351%	$40.1794	$40.18	$40.20	$40.20
Purchase #2	$78.47	6.413%	$83.5023	$83.50	$83.50	$83.50
Purchase #3	$88.62	8.133%	$95.8275	$95.83	$95.85	$95.80
Purchase #4	$195.61	13.534%	$222.0839	$222.08	$222.10	$222.10
Purchase #5	$222.49	7.261%	$238.645	$238.65	$238.65	$238.60
Purchase #6	$63.55	11.715%	$70.9949	$70.99	$71.00	$71.00
Purchase #7	$86.91	4.642%	$90.9444	$90.94	$90.95	$90.90
7 purchase totals =	$773.43		$842.1774	$842.17	$842.25	$842.10