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	$35.71	13.704%	$40.6037	$40.60	$40.60	$40.60
Purchase #2	$224.74	4.111%	$233.9791	$233.98	$234.00	$234.00
Purchase #3	$152.93	12.258%	$171.6762	$171.68	$171.70	$171.70
Purchase #4	$35.70	11.758%	$39.8976	$39.90	$39.90	$39.90
Purchase #5	$196.65	12.639%	$221.5046	$221.50	$221.50	$221.50
Purchase #6	$119.99	7.400%	$128.8693	$128.87	$128.85	$128.90
Purchase #7	$213.95	5.160%	$224.9898	$224.99	$225.00	$225.00
7 purchase totals =	$979.67		$1,061.5203	$1,061.52	$1,061.55	$1,061.60