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	$240.55	13.560%	$273.1686	$273.17	$273.15	$273.20
Purchase #2	$186.80	12.152%	$209.4999	$209.50	$209.50	$209.50
Purchase #3	$90.35	13.724%	$102.7496	$102.75	$102.75	$102.70
Purchase #4	$130.95	9.396%	$143.2541	$143.25	$143.25	$143.30
Purchase #5	$112.47	9.551%	$123.212	$123.21	$123.20	$123.20
Purchase #6	$238.86	3.471%	$247.1508	$247.15	$247.15	$247.20
Purchase #7	$131.96	9.794%	$144.8842	$144.88	$144.90	$144.90
7 purchase totals =	$1,131.94		$1,243.9192	$1,243.91	$1,243.90	$1,244.00