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	$49.95	13.752%	$56.8191	$56.82	$56.80	$56.80
Purchase #2	$40.67	9.681%	$44.6073	$44.61	$44.60	$44.60
Purchase #3	$191.80	8.177%	$207.4835	$207.48	$207.50	$207.50
Purchase #4	$90.48	3.345%	$93.5066	$93.51	$93.50	$93.50
Purchase #5	$148.58	8.296%	$160.9062	$160.91	$160.90	$160.90
Purchase #6	$229.68	11.221%	$255.4524	$255.45	$255.45	$255.50
Purchase #7	$181.94	10.255%	$200.5979	$200.60	$200.60	$200.60
7 purchase totals =	$933.10		$1,019.3730	$1,019.38	$1,019.35	$1,019.40