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 $58.73   8.200%   $63.5459   $63.55   $63.55   $63.50  
  Purchase #2 $233.97   11.844%   $261.6814   $261.68   $261.70   $261.70  
  Purchase #3 $23.56   11.685%   $26.313   $26.31   $26.30   $26.30  
  Purchase #4 $146.34   7.177%   $156.8428   $156.84   $156.85   $156.80  
  Purchase #5 $191.40   4.312%   $199.6532   $199.65   $199.65   $199.70  
  Purchase #6 $86.74   12.487%   $97.5712   $97.57   $97.55   $97.60  
  Purchase #7 $125.66   5.396%   $132.4406   $132.44   $132.45   $132.40  
  7 purchase totals = $866.40       $938.0481   $938.04   $938.05   $938.00