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 $244.57   6.726%   $261.0198   $261.02   $261.00   $261.00  
  Purchase #2 $61.37   6.655%   $65.4542   $65.45   $65.45   $65.50  
  Purchase #3 $125.28   8.552%   $135.9939   $135.99   $136.00   $136.00  
  Purchase #4 $56.45   7.514%   $60.6917   $60.69   $60.70   $60.70  
  Purchase #5 $56.50   8.358%   $61.2223   $61.22   $61.20   $61.20  
  Purchase #6 $201.75   4.795%   $211.4239   $211.42   $211.40   $211.40  
  Purchase #7 $29.97   4.624%   $31.3558   $31.36   $31.35   $31.40  
  7 purchase totals = $775.89       $827.1616   $827.15   $827.10   $827.20