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	$103.46	5.561%	$109.2134	$109.21	$109.20	$109.20
Purchase #2	$132.71	13.290%	$150.3472	$150.35	$150.35	$150.30
Purchase #3	$137.72	12.384%	$154.7752	$154.78	$154.80	$154.80
Purchase #4	$150.63	8.579%	$163.5525	$163.55	$163.55	$163.60
Purchase #5	$14.93	4.189%	$15.5554	$15.56	$15.55	$15.60
Purchase #6	$79.89	13.324%	$90.5345	$90.53	$90.55	$90.50
Purchase #7	$143.27	13.689%	$162.8822	$162.88	$162.90	$162.90
7 purchase totals =	$762.61		$846.8604	$846.86	$846.90	$846.90