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	$139.64	4.218%	$145.53	$145.53	$145.55	$145.50
Purchase #2	$68.73	11.139%	$76.3858	$76.39	$76.40	$76.40
Purchase #3	$82.85	9.536%	$90.7506	$90.75	$90.75	$90.80
Purchase #4	$20.62	6.113%	$21.8805	$21.88	$21.90	$21.90
Purchase #5	$194.86	10.292%	$214.915	$214.92	$214.90	$214.90
Purchase #6	$6.29	6.825%	$6.7193	$6.72	$6.70	$6.70
Purchase #7	$138.70	10.674%	$153.5048	$153.50	$153.50	$153.50
7 purchase totals =	$651.69		$709.6860	$709.69	$709.70	$709.70