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	$40.47	13.212%	$45.8169	$45.82	$45.80	$45.80
Purchase #2	$171.64	8.304%	$185.893	$185.89	$185.90	$185.90
Purchase #3	$164.68	10.178%	$181.4411	$181.44	$181.45	$181.40
Purchase #4	$123.27	13.660%	$140.1087	$140.11	$140.10	$140.10
Purchase #5	$226.60	12.847%	$255.7113	$255.71	$255.70	$255.70
Purchase #6	$143.56	5.333%	$151.2161	$151.22	$151.20	$151.20
Purchase #7	$31.53	11.545%	$35.1701	$35.17	$35.15	$35.20
7 purchase totals =	$901.75		$995.3572	$995.36	$995.30	$995.30