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	$122.44	3.300%	$126.4805	$126.48	$126.50	$126.50
Purchase #2	$175.47	5.615%	$185.3226	$185.32	$185.30	$185.30
Purchase #3	$224.37	7.474%	$241.1394	$241.14	$241.15	$241.10
Purchase #4	$167.48	13.596%	$190.2506	$190.25	$190.25	$190.30
Purchase #5	$83.89	7.406%	$90.1029	$90.10	$90.10	$90.10
Purchase #6	$25.84	11.126%	$28.715	$28.72	$28.70	$28.70
Purchase #7	$115.94	10.783%	$128.4418	$128.44	$128.45	$128.40
7 purchase totals =	$915.43		$990.4528	$990.45	$990.45	$990.40