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	$38.78	13.149%	$43.8792	$43.88	$43.90	$43.90
Purchase #2	$103.82	5.792%	$109.8333	$109.83	$109.85	$109.80
Purchase #3	$83.72	5.571%	$88.384	$88.38	$88.40	$88.40
Purchase #4	$47.62	11.123%	$52.9168	$52.92	$52.90	$52.90
Purchase #5	$25.32	4.359%	$26.4237	$26.42	$26.40	$26.40
Purchase #6	$188.28	8.248%	$203.8093	$203.81	$203.80	$203.80
Purchase #7	$169.50	10.336%	$187.0195	$187.02	$187.00	$187.00
7 purchase totals =	$657.04		$712.2658	$712.26	$712.25	$712.20