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	$131.29	10.365%	$144.8982	$144.90	$144.90	$144.90
Purchase #2	$77.97	3.426%	$80.6413	$80.64	$80.65	$80.60
Purchase #3	$175.35	8.665%	$190.5441	$190.54	$190.55	$190.50
Purchase #4	$14.31	7.339%	$15.3602	$15.36	$15.35	$15.40
Purchase #5	$190.79	9.796%	$209.4798	$209.48	$209.50	$209.50
Purchase #6	$103.86	5.787%	$109.8704	$109.87	$109.85	$109.90
Purchase #7	$137.75	13.126%	$155.8311	$155.83	$155.85	$155.80
7 purchase totals =	$831.32		$906.6251	$906.62	$906.65	$906.60