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	$98.89	4.636%	$103.4745	$103.47	$103.45	$103.50
Purchase #2	$35.78	6.779%	$38.2055	$38.21	$38.20	$38.20
Purchase #3	$220.97	9.456%	$241.8649	$241.86	$241.85	$241.90
Purchase #4	$65.94	6.579%	$70.2782	$70.28	$70.30	$70.30
Purchase #5	$213.72	8.463%	$231.8071	$231.81	$231.80	$231.80
Purchase #6	$172.48	12.799%	$194.5557	$194.56	$194.55	$194.60
Purchase #7	$237.30	10.550%	$262.3352	$262.34	$262.35	$262.30
7 purchase totals =	$1,045.08		$1,142.5211	$1,142.53	$1,142.50	$1,142.60