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	$249.90	11.832%	$279.4682	$279.47	$279.45	$279.50
Purchase #2	$85.52	11.827%	$95.6345	$95.63	$95.65	$95.60
Purchase #3	$249.86	4.782%	$261.8083	$261.81	$261.80	$261.80
Purchase #4	$70.70	5.594%	$74.655	$74.66	$74.65	$74.70
Purchase #5	$134.54	7.428%	$144.5336	$144.53	$144.55	$144.50
Purchase #6	$44.38	3.421%	$45.8982	$45.90	$45.90	$45.90
Purchase #7	$129.76	3.474%	$134.2679	$134.27	$134.25	$134.30
7 purchase totals =	$964.66		$1,036.2657	$1,036.27	$1,036.25	$1,036.30