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	$15.85	6.390%	$16.8628	$16.86	$16.85	$16.90
Purchase #2	$140.31	12.800%	$158.2697	$158.27	$158.25	$158.30
Purchase #3	$94.43	5.745%	$99.855	$99.86	$99.85	$99.90
Purchase #4	$190.48	12.490%	$214.271	$214.27	$214.25	$214.30
Purchase #5	$129.71	7.578%	$139.5394	$139.54	$139.55	$139.50
Purchase #6	$41.48	11.426%	$46.2195	$46.22	$46.20	$46.20
Purchase #7	$49.70	8.753%	$54.0502	$54.05	$54.05	$54.10
7 purchase totals =	$661.96		$729.0676	$729.07	$729.00	$729.20