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 $247.64   5.684%   $261.7159   $261.72   $261.70   $261.70  
  Purchase #2 $229.46   6.134%   $243.5351   $243.54   $243.55   $243.50  
  Purchase #3 $181.80   11.276%   $202.2998   $202.30   $202.30   $202.30  
  Purchase #4 $83.62   11.759%   $93.4529   $93.45   $93.45   $93.50  
  Purchase #5 $8.72   13.564%   $9.9028   $9.90   $9.90   $9.90  
  Purchase #6 $201.32   3.765%   $208.8997   $208.90   $208.90   $208.90  
  Purchase #7 $175.45   12.624%   $197.5988   $197.60   $197.60   $197.60  
  7 purchase totals = $1,128.01       $1,217.4050   $1,217.41   $1,217.40   $1,217.40