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	$16.95	4.424%	$17.6999	$17.70	$17.70	$17.70
Purchase #2	$74.27	5.736%	$78.5301	$78.53	$78.55	$78.50
Purchase #3	$89.65	8.667%	$97.42	$97.42	$97.40	$97.40
Purchase #4	$100.39	6.596%	$107.0117	$107.01	$107.00	$107.00
Purchase #5	$109.62	12.215%	$123.0101	$123.01	$123.00	$123.00
Purchase #6	$103.26	8.113%	$111.6375	$111.64	$111.65	$111.60
Purchase #7	$46.39	7.845%	$50.0293	$50.03	$50.05	$50.00
7 purchase totals =	$540.53		$585.3386	$585.34	$585.35	$585.20