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	$148.40	6.464%	$157.9926	$157.99	$158.00	$158.00
Purchase #2	$122.76	7.126%	$131.5079	$131.51	$131.50	$131.50
Purchase #3	$52.55	13.384%	$59.5833	$59.58	$59.60	$59.60
Purchase #4	$74.65	5.638%	$78.8588	$78.86	$78.85	$78.90
Purchase #5	$41.42	8.195%	$44.8144	$44.81	$44.80	$44.80
Purchase #6	$60.45	3.166%	$62.3638	$62.36	$62.35	$62.40
Purchase #7	$115.83	4.680%	$121.2508	$121.25	$121.25	$121.30
7 purchase totals =	$616.06		$656.3716	$656.36	$656.35	$656.50