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 $75.81   13.102%   $85.7426   $85.74   $85.75   $85.70  
  Purchase #2 $207.88   11.515%   $231.8174   $231.82   $231.80   $231.80  
  Purchase #3 $214.63   8.125%   $232.0687   $232.07   $232.05   $232.10  
  Purchase #4 $117.96   12.474%   $132.6743   $132.67   $132.65   $132.70  
  Purchase #5 $138.35   10.610%   $153.0289   $153.03   $153.05   $153.00  
  Purchase #6 $232.47   12.388%   $261.2684   $261.27   $261.25   $261.30  
  Purchase #7 $217.27   4.672%   $227.4209   $227.42   $227.40   $227.40  
  7 purchase totals = $1,204.37       $1,324.0212   $1,324.02   $1,323.95   $1,324.00