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 $9.37   5.429%   $9.8787   $9.88   $9.90   $9.90  
  Purchase #2 $10.38   3.564%   $10.7499   $10.75   $10.75   $10.70  
  Purchase #3 $180.53   9.698%   $198.0378   $198.04   $198.05   $198.00  
  Purchase #4 $109.62   7.214%   $117.528   $117.53   $117.55   $117.50  
  Purchase #5 $34.63   4.707%   $36.26   $36.26   $36.25   $36.30  
  Purchase #6 $66.86   3.451%   $69.1673   $69.17   $69.15   $69.20  
  Purchase #7 $205.39   9.149%   $224.1811   $224.18   $224.20   $224.20  
  7 purchase totals = $616.78       $665.8028   $665.81   $665.85   $665.80