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	$242.51	4.247%	$252.8094	$252.81	$252.80	$252.80
Purchase #2	$227.35	12.714%	$256.2553	$256.26	$256.25	$256.30
Purchase #3	$46.48	4.638%	$48.6357	$48.64	$48.65	$48.60
Purchase #4	$60.47	3.789%	$62.7612	$62.76	$62.75	$62.80
Purchase #5	$103.40	9.859%	$113.5942	$113.59	$113.60	$113.60
Purchase #6	$232.47	11.803%	$259.9084	$259.91	$259.90	$259.90
Purchase #7	$137.69	9.309%	$150.5076	$150.51	$150.50	$150.50
7 purchase totals =	$1,050.37		$1,144.4718	$1,144.48	$1,144.45	$1,144.50