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 $136.95   13.741%   $155.7683   $155.77   $155.75   $155.80  
  Purchase #2 $180.40   12.229%   $202.4611   $202.46   $202.45   $202.50  
  Purchase #3 $125.34   11.288%   $139.4884   $139.49   $139.50   $139.50  
  Purchase #4 $215.63   9.309%   $235.703   $235.70   $235.70   $235.70  
  Purchase #5 $45.77   5.838%   $48.4421   $48.44   $48.45   $48.40  
  Purchase #6 $58.91   3.451%   $60.943   $60.94   $60.95   $60.90  
  Purchase #7 $152.83   10.229%   $168.463   $168.46   $168.45   $168.50  
  7 purchase totals = $915.83       $1,011.2689   $1,011.26   $1,011.25   $1,011.30