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	$13.97	12.175%	$15.6708	$15.67	$15.65	$15.70
Purchase #2	$137.89	4.357%	$143.8979	$143.90	$143.90	$143.90
Purchase #3	$121.91	8.500%	$132.2724	$132.27	$132.25	$132.30
Purchase #4	$225.82	4.663%	$236.35	$236.35	$236.35	$236.40
Purchase #5	$40.47	7.702%	$43.587	$43.59	$43.60	$43.60
Purchase #6	$96.38	10.457%	$106.4585	$106.46	$106.45	$106.50
Purchase #7	$40.83	4.733%	$42.7625	$42.76	$42.75	$42.80
7 purchase totals =	$677.27		$720.9991	$721.00	$720.95	$721.20