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	$43.45	9.435%	$47.5495	$47.55	$47.55	$47.50
Purchase #2	$117.63	3.315%	$121.5294	$121.53	$121.55	$121.50
Purchase #3	$104.28	7.296%	$111.8883	$111.89	$111.90	$111.90
Purchase #4	$24.85	12.202%	$27.8822	$27.88	$27.90	$27.90
Purchase #5	$8.57	9.498%	$9.384	$9.38	$9.40	$9.40
Purchase #6	$60.47	10.495%	$66.8163	$66.82	$66.80	$66.80
Purchase #7	$105.40	7.584%	$113.3935	$113.39	$113.40	$113.40
7 purchase totals =	$464.65		$498.4432	$498.44	$498.50	$498.40