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	$126.60	12.388%	$142.2832	$142.28	$142.30	$142.30
Purchase #2	$105.74	12.419%	$118.8719	$118.87	$118.85	$118.90
Purchase #3	$172.38	8.712%	$187.3977	$187.40	$187.40	$187.40
Purchase #4	$195.83	11.585%	$218.5169	$218.52	$218.50	$218.50
Purchase #5	$229.42	12.245%	$257.5125	$257.51	$257.50	$257.50
Purchase #6	$58.91	13.870%	$67.0808	$67.08	$67.10	$67.10
Purchase #7	$35.65	12.336%	$40.0478	$40.05	$40.05	$40.00
7 purchase totals =	$924.53		$1,031.7108	$1,031.71	$1,031.70	$1,031.70