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	$19.43	7.563%	$20.8995	$20.90	$20.90	$20.90
Purchase #2	$151.25	5.376%	$159.3812	$159.38	$159.40	$159.40
Purchase #3	$47.63	10.147%	$52.463	$52.46	$52.45	$52.50
Purchase #4	$119.61	10.442%	$132.0997	$132.10	$132.10	$132.10
Purchase #5	$207.51	3.554%	$214.8849	$214.88	$214.90	$214.90
Purchase #6	$154.71	13.492%	$175.5835	$175.58	$175.60	$175.60
Purchase #7	$233.57	5.112%	$245.5101	$245.51	$245.50	$245.50
7 purchase totals =	$933.71		$1,000.8219	$1,000.81	$1,000.85	$1,000.90