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 $23.72   9.828%   $26.0512   $26.05   $26.05   $26.10  
  Purchase #2 $190.57   6.495%   $202.9475   $202.95   $202.95   $202.90  
  Purchase #3 $226.86   13.224%   $256.86   $256.86   $256.85   $256.90  
  Purchase #4 $122.95   13.482%   $139.5261   $139.53   $139.55   $139.50  
  Purchase #5 $194.91   8.871%   $212.2005   $212.20   $212.20   $212.20  
  Purchase #6 $50.77   11.194%   $56.4532   $56.45   $56.45   $56.50  
  Purchase #7 $247.78   5.376%   $261.1007   $261.10   $261.10   $261.10  
  7 purchase totals = $1,057.56       $1,155.1392   $1,155.14   $1,155.15   $1,155.20