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	$123.62	12.652%	$139.2604	$139.26	$139.25	$139.30
Purchase #2	$108.60	8.829%	$118.1883	$118.19	$118.20	$118.20
Purchase #3	$173.28	12.693%	$195.2744	$195.27	$195.25	$195.30
Purchase #4	$100.94	13.514%	$114.581	$114.58	$114.60	$114.60
Purchase #5	$40.77	4.301%	$42.5235	$42.52	$42.50	$42.50
Purchase #6	$176.35	11.314%	$196.3022	$196.30	$196.30	$196.30
Purchase #7	$203.54	10.607%	$225.1295	$225.13	$225.15	$225.10
7 purchase totals =	$927.10		$1,031.2593	$1,031.25	$1,031.25	$1,031.30