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	$56.44	5.471%	$59.5278	$59.53	$59.55	$59.50
Purchase #2	$73.50	10.200%	$80.997	$81.00	$81.00	$81.00
Purchase #3	$89.65	13.774%	$101.9984	$102.00	$102.00	$102.00
Purchase #4	$21.81	9.429%	$23.8665	$23.87	$23.85	$23.90
Purchase #5	$103.75	12.636%	$116.8599	$116.86	$116.85	$116.90
Purchase #6	$208.99	3.300%	$215.8867	$215.89	$215.90	$215.90
Purchase #7	$36.69	7.483%	$39.4355	$39.44	$39.45	$39.40
7 purchase totals =	$590.83		$638.5718	$638.59	$638.60	$638.60