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	$133.59	11.141%	$148.4733	$148.47	$148.45	$148.50
Purchase #2	$59.45	3.320%	$61.4237	$61.42	$61.40	$61.40
Purchase #3	$155.54	6.463%	$165.5926	$165.59	$165.60	$165.60
Purchase #4	$239.41	8.289%	$259.2547	$259.25	$259.25	$259.30
Purchase #5	$109.54	6.524%	$116.6864	$116.69	$116.70	$116.70
Purchase #6	$20.32	3.607%	$21.0529	$21.05	$21.05	$21.10
Purchase #7	$144.39	8.170%	$156.1867	$156.19	$156.20	$156.20
7 purchase totals =	$862.24		$928.6703	$928.66	$928.65	$928.80