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	$249.78	12.194%	$280.2382	$280.24	$280.25	$280.20
Purchase #2	$172.90	6.157%	$183.5455	$183.55	$183.55	$183.50
Purchase #3	$70.79	10.488%	$78.2145	$78.21	$78.20	$78.20
Purchase #4	$215.48	11.310%	$239.8508	$239.85	$239.85	$239.90
Purchase #5	$5.28	3.485%	$5.464	$5.46	$5.45	$5.50
Purchase #6	$205.85	13.569%	$233.7818	$233.78	$233.80	$233.80
Purchase #7	$10.58	12.182%	$11.8689	$11.87	$11.85	$11.90
7 purchase totals =	$930.66		$1,032.9637	$1,032.96	$1,032.95	$1,033.00