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	$186.59	10.305%	$205.8181	$205.82	$205.80	$205.80
Purchase #2	$247.58	13.105%	$280.0254	$280.03	$280.05	$280.00
Purchase #3	$166.44	7.828%	$179.4689	$179.47	$179.45	$179.50
Purchase #4	$151.93	9.304%	$166.0656	$166.07	$166.05	$166.10
Purchase #5	$247.46	13.745%	$281.4734	$281.47	$281.45	$281.50
Purchase #6	$242.42	5.863%	$256.6331	$256.63	$256.65	$256.60
Purchase #7	$21.48	12.204%	$24.1014	$24.10	$24.10	$24.10
7 purchase totals =	$1,263.90		$1,393.5859	$1,393.59	$1,393.55	$1,393.60