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	$131.55	5.831%	$139.2207	$139.22	$139.20	$139.20
Purchase #2	$44.26	11.470%	$49.3366	$49.34	$49.35	$49.30
Purchase #3	$65.94	9.667%	$72.3144	$72.31	$72.30	$72.30
Purchase #4	$43.81	8.835%	$47.6806	$47.68	$47.70	$47.70
Purchase #5	$18.28	10.407%	$20.1824	$20.18	$20.20	$20.20
Purchase #6	$102.50	4.269%	$106.8757	$106.88	$106.90	$106.90
Purchase #7	$153.48	7.254%	$164.6134	$164.61	$164.60	$164.60
7 purchase totals =	$559.82		$600.2238	$600.22	$600.25	$600.20