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	$138.66	11.365%	$154.4187	$154.42	$154.40	$154.40
Purchase #2	$71.39	10.340%	$78.7717	$78.77	$78.75	$78.80
Purchase #3	$164.55	3.360%	$170.0789	$170.08	$170.10	$170.10
Purchase #4	$40.83	4.480%	$42.6592	$42.66	$42.65	$42.70
Purchase #5	$212.57	12.280%	$238.6736	$238.67	$238.65	$238.70
Purchase #6	$62.38	11.583%	$69.6055	$69.61	$69.60	$69.60
Purchase #7	$126.83	8.164%	$137.1844	$137.18	$137.20	$137.20
7 purchase totals =	$817.21		$891.3920	$891.39	$891.35	$891.50