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	$131.60	10.628%	$145.5864	$145.59	$145.60	$145.60
Purchase #2	$166.82	4.813%	$174.849	$174.85	$174.85	$174.80
Purchase #3	$177.90	10.702%	$196.9389	$196.94	$196.95	$196.90
Purchase #4	$100.88	10.565%	$111.538	$111.54	$111.55	$111.50
Purchase #5	$203.50	4.473%	$212.6026	$212.60	$212.60	$212.60
Purchase #6	$28.29	12.310%	$31.7725	$31.77	$31.75	$31.80
Purchase #7	$28.78	3.527%	$29.7951	$29.80	$29.80	$29.80
7 purchase totals =	$837.77		$903.0825	$903.09	$903.10	$903.00