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	$99.70	11.786%	$111.4506	$111.45	$111.45	$111.50
Purchase #2	$145.94	10.604%	$161.4155	$161.42	$161.40	$161.40
Purchase #3	$228.89	4.427%	$239.023	$239.02	$239.00	$239.00
Purchase #4	$29.63	9.820%	$32.5397	$32.54	$32.55	$32.50
Purchase #5	$120.46	5.746%	$127.3816	$127.38	$127.40	$127.40
Purchase #6	$116.59	8.520%	$126.5235	$126.52	$126.50	$126.50
Purchase #7	$145.79	3.227%	$150.4946	$150.49	$150.50	$150.50
7 purchase totals =	$887.00		$948.8285	$948.82	$948.80	$948.80