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	$27.85	6.259%	$29.5931	$29.59	$29.60	$29.60
Purchase #2	$24.40	7.752%	$26.2915	$26.29	$26.30	$26.30
Purchase #3	$79.70	7.602%	$85.7588	$85.76	$85.75	$85.80
Purchase #4	$150.79	13.486%	$171.1255	$171.13	$171.15	$171.10
Purchase #5	$142.52	5.661%	$150.5881	$150.59	$150.60	$150.60
Purchase #6	$98.49	13.716%	$111.9989	$112.00	$112.00	$112.00
Purchase #7	$198.91	13.382%	$225.5281	$225.53	$225.55	$225.50
7 purchase totals =	$722.66		$800.8840	$800.89	$800.95	$800.90