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	$36.93	10.703%	$40.8826	$40.88	$40.90	$40.90
Purchase #2	$31.38	13.257%	$35.54	$35.54	$35.55	$35.50
Purchase #3	$94.95	10.509%	$104.9283	$104.93	$104.95	$104.90
Purchase #4	$97.71	10.201%	$107.6774	$107.68	$107.70	$107.70
Purchase #5	$198.60	8.295%	$215.0739	$215.07	$215.05	$215.10
Purchase #6	$69.77	13.141%	$78.9385	$78.94	$78.95	$78.90
Purchase #7	$171.51	11.362%	$190.997	$191.00	$191.00	$191.00
7 purchase totals =	$700.85		$774.0377	$774.04	$774.10	$774.00