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	$112.47	9.587%	$123.2525	$123.25	$123.25	$123.30
Purchase #2	$47.75	8.365%	$51.7443	$51.74	$51.75	$51.70
Purchase #3	$122.82	13.605%	$139.5297	$139.53	$139.55	$139.50
Purchase #4	$93.45	11.580%	$104.2715	$104.27	$104.25	$104.30
Purchase #5	$75.25	11.166%	$83.6524	$83.65	$83.65	$83.70
Purchase #6	$100.57	8.398%	$109.0159	$109.02	$109.00	$109.00
Purchase #7	$211.42	13.482%	$239.9236	$239.92	$239.90	$239.90
7 purchase totals =	$763.73		$851.3899	$851.38	$851.35	$851.40