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	$108.88	13.235%	$123.2903	$123.29	$123.30	$123.30
Purchase #2	$131.90	13.436%	$149.6221	$149.62	$149.60	$149.60
Purchase #3	$104.55	11.172%	$116.2303	$116.23	$116.25	$116.20
Purchase #4	$12.63	6.296%	$13.4252	$13.43	$13.45	$13.40
Purchase #5	$53.28	11.431%	$59.3704	$59.37	$59.35	$59.40
Purchase #6	$43.94	12.793%	$49.5612	$49.56	$49.55	$49.60
Purchase #7	$117.32	7.722%	$126.3795	$126.38	$126.40	$126.40
7 purchase totals =	$572.50		$637.8790	$637.88	$637.90	$637.90