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	$18.67	11.265%	$20.7732	$20.77	$20.75	$20.80
Purchase #2	$104.31	6.865%	$111.4709	$111.47	$111.45	$111.50
Purchase #3	$130.52	3.154%	$134.6366	$134.64	$134.65	$134.60
Purchase #4	$18.99	13.842%	$21.6186	$21.62	$21.60	$21.60
Purchase #5	$44.62	6.840%	$47.672	$47.67	$47.65	$47.70
Purchase #6	$155.93	11.595%	$174.0101	$174.01	$174.00	$174.00
Purchase #7	$78.27	4.263%	$81.6067	$81.61	$81.60	$81.60
7 purchase totals =	$551.31		$591.7881	$591.79	$591.70	$591.80