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	$175.55	4.527%	$183.4971	$183.50	$183.50	$183.50
Purchase #2	$222.63	4.870%	$233.4721	$233.47	$233.45	$233.50
Purchase #3	$145.37	13.724%	$165.3206	$165.32	$165.30	$165.30
Purchase #4	$239.88	6.451%	$255.3547	$255.35	$255.35	$255.40
Purchase #5	$206.42	6.152%	$219.119	$219.12	$219.10	$219.10
Purchase #6	$209.82	13.429%	$237.9967	$238.00	$238.00	$238.00
Purchase #7	$113.37	10.786%	$125.5981	$125.60	$125.60	$125.60
7 purchase totals =	$1,313.04		$1,420.3583	$1,420.36	$1,420.30	$1,420.40