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	$231.29	12.794%	$260.8812	$260.88	$260.90	$260.90
Purchase #2	$40.42	10.182%	$44.5356	$44.54	$44.55	$44.50
Purchase #3	$144.97	4.808%	$151.9402	$151.94	$151.95	$151.90
Purchase #4	$239.78	4.457%	$250.467	$250.47	$250.45	$250.50
Purchase #5	$45.34	9.293%	$49.5534	$49.55	$49.55	$49.60
Purchase #6	$76.81	5.175%	$80.7849	$80.78	$80.80	$80.80
Purchase #7	$45.78	5.561%	$48.3258	$48.33	$48.35	$48.30
7 purchase totals =	$824.39		$886.4881	$886.49	$886.55	$886.50