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	$116.59	9.285%	$127.4154	$127.42	$127.40	$127.40
Purchase #2	$156.25	12.726%	$176.1344	$176.13	$176.15	$176.10
Purchase #3	$10.54	4.795%	$11.0454	$11.05	$11.05	$11.00
Purchase #4	$120.64	10.104%	$132.8295	$132.83	$132.85	$132.80
Purchase #5	$63.97	4.332%	$66.7412	$66.74	$66.75	$66.70
Purchase #6	$37.78	9.440%	$41.3464	$41.35	$41.35	$41.30
Purchase #7	$30.64	7.219%	$32.8519	$32.85	$32.85	$32.90
7 purchase totals =	$536.41		$588.3642	$588.37	$588.40	$588.20