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	$45.38	12.289%	$50.9567	$50.96	$50.95	$51.00
Purchase #2	$32.97	4.671%	$34.51	$34.51	$34.50	$34.50
Purchase #3	$95.38	9.194%	$104.1492	$104.15	$104.15	$104.10
Purchase #4	$120.27	9.401%	$131.5766	$131.58	$131.60	$131.60
Purchase #5	$94.43	8.478%	$102.4358	$102.44	$102.45	$102.40
Purchase #6	$140.54	4.193%	$146.4328	$146.43	$146.45	$146.40
Purchase #7	$172.59	7.203%	$185.0217	$185.02	$185.00	$185.00
7 purchase totals =	$701.56		$755.0828	$755.09	$755.10	$755.00