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 $86.63   8.819%   $94.2699   $94.27   $94.25   $94.30  
  Purchase #2 $183.70   13.187%   $207.9245   $207.92   $207.90   $207.90  
  Purchase #3 $119.89   4.504%   $125.2898   $125.29   $125.30   $125.30  
  Purchase #4 $130.64   4.145%   $136.055   $136.06   $136.05   $136.10  
  Purchase #5 $88.47   10.391%   $97.6629   $97.66   $97.65   $97.70  
  Purchase #6 $27.91   6.526%   $29.7314   $29.73   $29.75   $29.70  
  Purchase #7 $199.97   8.614%   $217.1954   $217.20   $217.20   $217.20  
  7 purchase totals = $837.21       $908.1289   $908.13   $908.10   $908.20