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	$111.29	7.798%	$119.9684	$119.97	$119.95	$120.00
Purchase #2	$40.66	4.709%	$42.5747	$42.57	$42.55	$42.60
Purchase #3	$105.98	8.842%	$115.3508	$115.35	$115.35	$115.40
Purchase #4	$129.28	12.354%	$145.2513	$145.25	$145.25	$145.30
Purchase #5	$107.28	3.855%	$111.4156	$111.42	$111.40	$111.40
Purchase #6	$32.98	7.577%	$35.4789	$35.48	$35.50	$35.50
Purchase #7	$44.27	7.238%	$47.4743	$47.47	$47.45	$47.50
7 purchase totals =	$571.74		$617.5140	$617.51	$617.45	$617.70