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 $61.83   7.653%   $66.5618   $66.56   $66.55   $66.60  
  Purchase #2 $22.57   7.581%   $24.281   $24.28   $24.30   $24.30  
  Purchase #3 $207.45   12.121%   $232.595   $232.60   $232.60   $232.60  
  Purchase #4 $181.68   3.542%   $188.1151   $188.12   $188.10   $188.10  
  Purchase #5 $68.99   3.172%   $71.1784   $71.18   $71.20   $71.20  
  Purchase #6 $22.88   3.424%   $23.6634   $23.66   $23.65   $23.70  
  Purchase #7 $229.27   13.626%   $260.5103   $260.51   $260.50   $260.50  
  7 purchase totals = $794.67       $866.9050   $866.91   $866.90   $867.00