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	$38.35	3.211%	$39.5814	$39.58	$39.60	$39.60
Purchase #2	$127.50	9.691%	$139.856	$139.86	$139.85	$139.90
Purchase #3	$187.64	4.765%	$196.581	$196.58	$196.60	$196.60
Purchase #4	$35.67	6.770%	$38.0849	$38.08	$38.10	$38.10
Purchase #5	$172.27	7.693%	$185.5227	$185.52	$185.50	$185.50
Purchase #6	$48.59	10.427%	$53.6565	$53.66	$53.65	$53.70
Purchase #7	$44.68	6.293%	$47.4917	$47.49	$47.50	$47.50
7 purchase totals =	$654.70		$700.7742	$700.77	$700.80	$700.90