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	$150.95	10.490%	$166.7847	$166.78	$166.80	$166.80
Purchase #2	$16.37	3.282%	$16.9073	$16.91	$16.90	$16.90
Purchase #3	$134.72	7.384%	$144.6677	$144.67	$144.65	$144.70
Purchase #4	$80.93	11.705%	$90.4029	$90.40	$90.40	$90.40
Purchase #5	$228.46	4.837%	$239.5106	$239.51	$239.50	$239.50
Purchase #6	$127.25	13.460%	$144.3779	$144.38	$144.40	$144.40
Purchase #7	$106.50	10.660%	$117.8529	$117.85	$117.85	$117.90
7 purchase totals =	$845.18		$920.5040	$920.50	$920.50	$920.60