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	$82.55	9.765%	$90.611	$90.61	$90.60	$90.60
Purchase #2	$227.82	5.738%	$240.8923	$240.89	$240.90	$240.90
Purchase #3	$18.94	12.669%	$21.3395	$21.34	$21.35	$21.30
Purchase #4	$14.74	4.807%	$15.4486	$15.45	$15.45	$15.40
Purchase #5	$183.58	3.583%	$190.1577	$190.16	$190.15	$190.20
Purchase #6	$239.73	13.350%	$271.734	$271.73	$271.75	$271.70
Purchase #7	$29.57	11.255%	$32.8981	$32.90	$32.90	$32.90
7 purchase totals =	$796.93		$863.0812	$863.08	$863.10	$863.00