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	$27.65	12.542%	$31.1179	$31.12	$31.10	$31.10
Purchase #2	$20.71	5.531%	$21.8555	$21.86	$21.85	$21.90
Purchase #3	$65.74	11.510%	$73.3067	$73.31	$73.30	$73.30
Purchase #4	$66.82	9.289%	$73.0269	$73.03	$73.05	$73.00
Purchase #5	$91.25	12.458%	$102.6179	$102.62	$102.60	$102.60
Purchase #6	$192.80	4.105%	$200.7144	$200.71	$200.70	$200.70
Purchase #7	$50.81	6.855%	$54.293	$54.29	$54.30	$54.30
7 purchase totals =	$515.78		$556.9323	$556.94	$556.90	$556.90