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 $54.60   13.203%   $61.8088   $61.81   $61.80   $61.80  
  Purchase #2 $139.47   8.669%   $151.5607   $151.56   $151.55   $151.60  
  Purchase #3 $57.51   4.653%   $60.1859   $60.19   $60.20   $60.20  
  Purchase #4 $232.49   6.285%   $247.102   $247.10   $247.10   $247.10  
  Purchase #5 $12.99   13.449%   $14.737   $14.74   $14.75   $14.70  
  Purchase #6 $236.90   10.534%   $261.855   $261.86   $261.85   $261.90  
  Purchase #7 $136.79   13.235%   $154.8942   $154.89   $154.90   $154.90  
  7 purchase totals = $870.75       $952.1436   $952.15   $952.15   $952.20