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	$240.40	12.528%	$270.5173	$270.52	$270.50	$270.50
Purchase #2	$81.55	10.791%	$90.3501	$90.35	$90.35	$90.40
Purchase #3	$91.61	11.831%	$102.4484	$102.45	$102.45	$102.40
Purchase #4	$142.50	11.561%	$158.9744	$158.97	$158.95	$159.00
Purchase #5	$7.45	5.317%	$7.8461	$7.85	$7.85	$7.80
Purchase #6	$213.35	12.707%	$240.4604	$240.46	$240.45	$240.50
Purchase #7	$125.51	9.110%	$136.944	$136.94	$136.95	$136.90
7 purchase totals =	$902.37		$1,007.5407	$1,007.54	$1,007.50	$1,007.50