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	$37.93	7.482%	$40.7679	$40.77	$40.75	$40.80
Purchase #2	$128.62	11.713%	$143.6853	$143.69	$143.70	$143.70
Purchase #3	$249.52	9.117%	$272.2687	$272.27	$272.25	$272.30
Purchase #4	$16.83	3.339%	$17.392	$17.39	$17.40	$17.40
Purchase #5	$54.98	12.585%	$61.8992	$61.90	$61.90	$61.90
Purchase #6	$239.85	11.851%	$268.2746	$268.27	$268.25	$268.30
Purchase #7	$154.65	12.636%	$174.1916	$174.19	$174.20	$174.20
7 purchase totals =	$882.38		$978.4793	$978.48	$978.45	$978.60