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	$123.45	11.381%	$137.4998	$137.50	$137.50	$137.50
Purchase #2	$102.57	10.347%	$113.1829	$113.18	$113.20	$113.20
Purchase #3	$228.45	12.726%	$257.5225	$257.52	$257.50	$257.50
Purchase #4	$164.72	10.790%	$182.4933	$182.49	$182.50	$182.50
Purchase #5	$199.32	4.653%	$208.5944	$208.59	$208.60	$208.60
Purchase #6	$103.77	12.627%	$116.873	$116.87	$116.85	$116.90
Purchase #7	$167.89	9.790%	$184.3264	$184.33	$184.35	$184.30
7 purchase totals =	$1,090.17		$1,200.4923	$1,200.48	$1,200.50	$1,200.50