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	$103.26	13.148%	$116.8366	$116.84	$116.85	$116.80
Purchase #2	$136.33	10.275%	$150.3379	$150.34	$150.35	$150.30
Purchase #3	$136.62	4.283%	$142.4714	$142.47	$142.45	$142.50
Purchase #4	$45.79	12.777%	$51.6406	$51.64	$51.65	$51.60
Purchase #5	$137.64	13.723%	$156.5283	$156.53	$156.55	$156.50
Purchase #6	$52.91	5.364%	$55.7481	$55.75	$55.75	$55.70
Purchase #7	$192.47	12.873%	$217.2467	$217.25	$217.25	$217.20
7 purchase totals =	$805.02		$890.8096	$890.82	$890.85	$890.60