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	$231.27	10.424%	$255.3776	$255.38	$255.40	$255.40
Purchase #2	$217.82	13.180%	$246.5287	$246.53	$246.55	$246.50
Purchase #3	$79.35	12.643%	$89.3822	$89.38	$89.40	$89.40
Purchase #4	$134.39	7.493%	$144.4598	$144.46	$144.45	$144.50
Purchase #5	$213.52	12.228%	$239.6292	$239.63	$239.65	$239.60
Purchase #6	$80.54	3.520%	$83.375	$83.38	$83.40	$83.40
Purchase #7	$34.25	12.621%	$38.5727	$38.57	$38.55	$38.60
7 purchase totals =	$991.14		$1,097.3252	$1,097.33	$1,097.40	$1,097.40