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	$153.71	9.265%	$167.9512	$167.95	$167.95	$168.00
Purchase #2	$100.98	8.245%	$109.3058	$109.31	$109.30	$109.30
Purchase #3	$62.78	10.425%	$69.3248	$69.32	$69.30	$69.30
Purchase #4	$166.94	3.849%	$173.3655	$173.37	$173.35	$173.40
Purchase #5	$32.83	12.414%	$36.9055	$36.91	$36.90	$36.90
Purchase #6	$38.60	4.827%	$40.4632	$40.46	$40.45	$40.50
Purchase #7	$117.68	5.587%	$124.2548	$124.25	$124.25	$124.30
7 purchase totals =	$673.52		$721.5708	$721.57	$721.50	$721.70