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	$96.67	12.364%	$108.6223	$108.62	$108.60	$108.60
Purchase #2	$134.52	7.732%	$144.9211	$144.92	$144.90	$144.90
Purchase #3	$186.78	9.598%	$204.7071	$204.71	$204.70	$204.70
Purchase #4	$196.52	5.808%	$207.9339	$207.93	$207.95	$207.90
Purchase #5	$38.95	4.402%	$40.6646	$40.66	$40.65	$40.70
Purchase #6	$200.70	4.758%	$210.2493	$210.25	$210.25	$210.20
Purchase #7	$108.75	13.523%	$123.4563	$123.46	$123.45	$123.50
7 purchase totals =	$962.89		$1,040.5546	$1,040.55	$1,040.50	$1,040.50