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	$28.60	13.603%	$32.4905	$32.49	$32.50	$32.50
Purchase #2	$153.92	7.128%	$164.8914	$164.89	$164.90	$164.90
Purchase #3	$107.85	9.129%	$117.6956	$117.70	$117.70	$117.70
Purchase #4	$117.70	7.652%	$126.7064	$126.71	$126.70	$126.70
Purchase #5	$38.57	5.274%	$40.6042	$40.60	$40.60	$40.60
Purchase #6	$162.74	9.661%	$178.4623	$178.46	$178.45	$178.50
Purchase #7	$92.48	8.471%	$100.314	$100.31	$100.30	$100.30
7 purchase totals =	$701.86		$761.1644	$761.16	$761.15	$761.20