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	$239.40	13.564%	$271.8722	$271.87	$271.85	$271.90
Purchase #2	$56.56	4.750%	$59.2466	$59.25	$59.25	$59.20
Purchase #3	$246.51	11.679%	$275.2999	$275.30	$275.30	$275.30
Purchase #4	$81.25	5.583%	$85.7862	$85.79	$85.80	$85.80
Purchase #5	$116.91	12.163%	$131.1298	$131.13	$131.15	$131.10
Purchase #6	$44.98	7.546%	$48.3742	$48.37	$48.35	$48.40
Purchase #7	$206.51	4.329%	$215.4498	$215.45	$215.45	$215.40
7 purchase totals =	$992.12		$1,087.1587	$1,087.16	$1,087.15	$1,087.10