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	$211.91	7.337%	$227.4578	$227.46	$227.45	$227.50
Purchase #2	$220.66	10.416%	$243.6439	$243.64	$243.65	$243.60
Purchase #3	$122.50	10.583%	$135.4642	$135.46	$135.45	$135.50
Purchase #4	$72.50	11.850%	$81.0913	$81.09	$81.10	$81.10
Purchase #5	$16.40	11.441%	$18.2763	$18.28	$18.30	$18.30
Purchase #6	$43.72	3.109%	$45.0793	$45.08	$45.10	$45.10
Purchase #7	$76.72	8.849%	$83.509	$83.51	$83.50	$83.50
7 purchase totals =	$764.41		$834.5218	$834.52	$834.55	$834.60