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	$11.64	10.130%	$12.8191	$12.82	$12.80	$12.80
Purchase #2	$213.49	12.358%	$239.8731	$239.87	$239.85	$239.90
Purchase #3	$111.32	4.210%	$116.0066	$116.01	$116.00	$116.00
Purchase #4	$45.72	3.687%	$47.4057	$47.41	$47.40	$47.40
Purchase #5	$138.83	8.342%	$150.4112	$150.41	$150.40	$150.40
Purchase #6	$120.89	12.654%	$136.1874	$136.19	$136.20	$136.20
Purchase #7	$81.54	9.713%	$89.46	$89.46	$89.45	$89.50
7 purchase totals =	$723.43		$792.1631	$792.17	$792.10	$792.20