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	$134.84	3.393%	$139.4151	$139.42	$139.40	$139.40
Purchase #2	$75.98	3.178%	$78.3946	$78.39	$78.40	$78.40
Purchase #3	$123.98	12.301%	$139.2308	$139.23	$139.25	$139.20
Purchase #4	$99.47	12.141%	$111.5467	$111.55	$111.55	$111.50
Purchase #5	$240.28	9.143%	$262.2488	$262.25	$262.25	$262.20
Purchase #6	$31.68	10.655%	$35.0555	$35.06	$35.05	$35.10
Purchase #7	$199.89	13.106%	$226.0876	$226.09	$226.10	$226.10
7 purchase totals =	$906.12		$991.9791	$991.99	$992.00	$991.90