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	$42.81	5.583%	$45.2001	$45.20	$45.20	$45.20
Purchase #2	$186.60	7.291%	$200.205	$200.21	$200.20	$200.20
Purchase #3	$35.88	12.195%	$40.2556	$40.26	$40.25	$40.30
Purchase #4	$214.98	5.799%	$227.4467	$227.45	$227.45	$227.40
Purchase #5	$193.65	6.252%	$205.757	$205.76	$205.75	$205.80
Purchase #6	$183.89	3.780%	$190.841	$190.84	$190.85	$190.80
Purchase #7	$18.43	9.789%	$20.2341	$20.23	$20.25	$20.20
7 purchase totals =	$876.24		$929.9395	$929.95	$929.95	$929.90