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 $174.81   12.828%   $197.2346   $197.23   $197.25   $197.20  
  Purchase #2 $102.52   3.116%   $105.7145   $105.71   $105.70   $105.70  
  Purchase #3 $239.86   7.348%   $257.4849   $257.48   $257.50   $257.50  
  Purchase #4 $213.94   8.712%   $232.5785   $232.58   $232.60   $232.60  
  Purchase #5 $80.67   6.692%   $86.0684   $86.07   $86.05   $86.10  
  Purchase #6 $209.27   10.766%   $231.8   $231.80   $231.80   $231.80  
  Purchase #7 $238.98   9.497%   $261.6759   $261.68   $261.70   $261.70  
  7 purchase totals = $1,260.05       $1,372.5568   $1,372.55   $1,372.60   $1,372.60