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	$236.40	9.601%	$259.0968	$259.10	$259.10	$259.10
Purchase #2	$122.49	10.164%	$134.9399	$134.94	$134.95	$134.90
Purchase #3	$19.45	11.302%	$21.6482	$21.65	$21.65	$21.60
Purchase #4	$148.62	13.289%	$168.3701	$168.37	$168.35	$168.40
Purchase #5	$96.48	7.120%	$103.3494	$103.35	$103.35	$103.30
Purchase #6	$91.86	12.406%	$103.2562	$103.26	$103.25	$103.30
Purchase #7	$57.39	3.274%	$59.2689	$59.27	$59.25	$59.30
7 purchase totals =	$772.69		$849.9295	$849.94	$849.90	$849.90