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	$45.31	3.239%	$46.7776	$46.78	$46.80	$46.80
Purchase #2	$103.97	13.371%	$117.8718	$117.87	$117.85	$117.90
Purchase #3	$126.59	9.710%	$138.8819	$138.88	$138.90	$138.90
Purchase #4	$122.92	13.182%	$139.1233	$139.12	$139.10	$139.10
Purchase #5	$82.84	8.652%	$90.0073	$90.01	$90.00	$90.00
Purchase #6	$226.57	10.743%	$250.9104	$250.91	$250.90	$250.90
Purchase #7	$27.89	12.492%	$31.374	$31.37	$31.35	$31.40
7 purchase totals =	$736.09		$814.9463	$814.94	$814.90	$815.00