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	$233.61	9.245%	$255.2072	$255.21	$255.20	$255.20
Purchase #2	$28.50	8.799%	$31.0077	$31.01	$31.00	$31.00
Purchase #3	$41.48	7.567%	$44.6188	$44.62	$44.60	$44.60
Purchase #4	$93.66	12.720%	$105.5736	$105.57	$105.55	$105.60
Purchase #5	$104.43	11.121%	$116.0437	$116.04	$116.05	$116.00
Purchase #6	$74.48	5.492%	$78.5704	$78.57	$78.55	$78.60
Purchase #7	$84.55	8.148%	$91.4391	$91.44	$91.45	$91.40
7 purchase totals =	$660.71		$722.4605	$722.46	$722.40	$722.40