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	$15.63	8.218%	$16.9145	$16.91	$16.90	$16.90
Purchase #2	$150.85	9.104%	$164.5834	$164.58	$164.60	$164.60
Purchase #3	$133.95	3.374%	$138.4695	$138.47	$138.45	$138.50
Purchase #4	$59.55	10.770%	$65.9635	$65.96	$65.95	$66.00
Purchase #5	$196.92	12.509%	$221.5527	$221.55	$221.55	$221.60
Purchase #6	$71.38	12.713%	$80.4545	$80.45	$80.45	$80.50
Purchase #7	$81.44	4.375%	$85.003	$85.00	$85.00	$85.00
7 purchase totals =	$709.72		$772.9411	$772.92	$772.90	$773.10