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	$60.87	7.767%	$65.5978	$65.60	$65.60	$65.60
Purchase #2	$160.88	8.601%	$174.7173	$174.72	$174.70	$174.70
Purchase #3	$38.65	4.791%	$40.5017	$40.50	$40.50	$40.50
Purchase #4	$126.83	11.106%	$140.9157	$140.92	$140.90	$140.90
Purchase #5	$248.88	6.308%	$264.5794	$264.58	$264.60	$264.60
Purchase #6	$102.98	13.585%	$116.9698	$116.97	$116.95	$117.00
Purchase #7	$182.82	5.495%	$192.866	$192.87	$192.85	$192.90
7 purchase totals =	$921.91		$996.1477	$996.16	$996.10	$996.20