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	$15.25	11.441%	$16.9948	$16.99	$17.00	$17.00
Purchase #2	$185.89	4.627%	$194.4911	$194.49	$194.50	$194.50
Purchase #3	$52.51	12.392%	$59.017	$59.02	$59.00	$59.00
Purchase #4	$107.47	4.295%	$112.0858	$112.09	$112.10	$112.10
Purchase #5	$81.32	12.537%	$91.5151	$91.52	$91.50	$91.50
Purchase #6	$139.59	13.210%	$158.0298	$158.03	$158.05	$158.00
Purchase #7	$220.51	11.221%	$245.2534	$245.25	$245.25	$245.30
7 purchase totals =	$802.54		$877.3870	$877.39	$877.40	$877.40