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	$59.25	12.157%	$66.453	$66.45	$66.45	$66.50
Purchase #2	$90.53	10.791%	$100.2991	$100.30	$100.30	$100.30
Purchase #3	$142.86	5.662%	$150.9487	$150.95	$150.95	$150.90
Purchase #4	$117.81	12.385%	$132.4008	$132.40	$132.40	$132.40
Purchase #5	$74.87	4.545%	$78.2728	$78.27	$78.25	$78.30
Purchase #6	$157.86	6.149%	$167.5668	$167.57	$167.55	$167.60
Purchase #7	$130.81	10.833%	$144.9806	$144.98	$145.00	$145.00
7 purchase totals =	$773.99		$840.9218	$840.92	$840.90	$841.00