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	$36.28	12.416%	$40.7845	$40.78	$40.80	$40.80
Purchase #2	$129.89	12.735%	$146.4315	$146.43	$146.45	$146.40
Purchase #3	$116.77	12.157%	$130.9657	$130.97	$130.95	$131.00
Purchase #4	$72.93	7.156%	$78.1489	$78.15	$78.15	$78.10
Purchase #5	$164.36	11.734%	$183.646	$183.65	$183.65	$183.60
Purchase #6	$50.98	5.602%	$53.8359	$53.84	$53.85	$53.80
Purchase #7	$185.54	12.434%	$208.61	$208.61	$208.60	$208.60
7 purchase totals =	$756.75		$842.4225	$842.43	$842.45	$842.30