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	$238.50	13.394%	$270.4447	$270.44	$270.45	$270.40
Purchase #2	$59.91	11.727%	$66.9356	$66.94	$66.95	$66.90
Purchase #3	$143.44	5.118%	$150.7813	$150.78	$150.80	$150.80
Purchase #4	$214.91	11.589%	$239.8159	$239.82	$239.80	$239.80
Purchase #5	$33.48	6.704%	$35.7245	$35.72	$35.70	$35.70
Purchase #6	$108.83	13.708%	$123.7484	$123.75	$123.75	$123.70
Purchase #7	$95.62	9.233%	$104.4486	$104.45	$104.45	$104.40
7 purchase totals =	$894.69		$991.8990	$991.90	$991.90	$991.70