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	$5.30	12.342%	$5.9541	$5.95	$5.95	$6.00
Purchase #2	$146.39	4.152%	$152.4681	$152.47	$152.45	$152.50
Purchase #3	$205.78	11.237%	$228.9035	$228.90	$228.90	$228.90
Purchase #4	$223.25	5.524%	$235.5823	$235.58	$235.60	$235.60
Purchase #5	$16.50	13.696%	$18.7598	$18.76	$18.75	$18.80
Purchase #6	$117.55	10.484%	$129.8739	$129.87	$129.85	$129.90
Purchase #7	$85.87	5.850%	$90.8934	$90.89	$90.90	$90.90
7 purchase totals =	$800.64		$862.4351	$862.42	$862.40	$862.60