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	$53.29	11.395%	$59.3624	$59.36	$59.35	$59.40
Purchase #2	$25.67	13.570%	$29.1534	$29.15	$29.15	$29.20
Purchase #3	$53.53	4.371%	$55.8698	$55.87	$55.85	$55.90
Purchase #4	$56.55	12.208%	$63.4536	$63.45	$63.45	$63.50
Purchase #5	$124.85	5.844%	$132.1462	$132.15	$132.15	$132.10
Purchase #6	$131.56	6.433%	$140.0233	$140.02	$140.00	$140.00
Purchase #7	$153.65	7.335%	$164.9202	$164.92	$164.90	$164.90
7 purchase totals =	$599.10		$644.9289	$644.92	$644.85	$645.00