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	$20.47	4.669%	$21.4257	$21.43	$21.45	$21.40
Purchase #2	$91.43	3.691%	$94.8047	$94.80	$94.80	$94.80
Purchase #3	$55.63	7.375%	$59.7327	$59.73	$59.75	$59.70
Purchase #4	$92.75	11.420%	$103.3421	$103.34	$103.35	$103.30
Purchase #5	$187.78	8.660%	$204.0417	$204.04	$204.05	$204.00
Purchase #6	$87.54	3.457%	$90.5663	$90.57	$90.55	$90.60
Purchase #7	$135.40	5.365%	$142.6642	$142.66	$142.65	$142.70
7 purchase totals =	$671.00		$716.5774	$716.57	$716.60	$716.50