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	$19.59	3.468%	$20.2694	$20.27	$20.25	$20.30
Purchase #2	$90.87	11.237%	$101.0811	$101.08	$101.10	$101.10
Purchase #3	$129.59	12.710%	$146.0609	$146.06	$146.05	$146.10
Purchase #4	$247.71	10.803%	$274.4701	$274.47	$274.45	$274.50
Purchase #5	$27.66	6.857%	$29.5566	$29.56	$29.55	$29.60
Purchase #6	$181.30	4.594%	$189.6289	$189.63	$189.65	$189.60
Purchase #7	$226.99	12.532%	$255.4364	$255.44	$255.45	$255.40
7 purchase totals =	$923.71		$1,016.5034	$1,016.51	$1,016.50	$1,016.60