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 $125.98   10.745%   $139.5166   $139.52   $139.50   $139.50  
  Purchase #2 $49.35   13.687%   $56.1045   $56.10   $56.10   $56.10  
  Purchase #3 $242.36   7.690%   $260.9975   $261.00   $261.00   $261.00  
  Purchase #4 $35.46   11.785%   $39.639   $39.64   $39.65   $39.60  
  Purchase #5 $222.75   8.413%   $241.49   $241.49   $241.50   $241.50  
  Purchase #6 $201.74   6.439%   $214.73   $214.73   $214.75   $214.70  
  Purchase #7 $61.36   10.773%   $67.9703   $67.97   $67.95   $68.00  
  7 purchase totals = $939.00       $1,020.4479   $1,020.45   $1,020.45   $1,020.40