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 $60.53   12.799%   $68.2772   $68.28   $68.30   $68.30  
  Purchase #2 $224.26   5.229%   $235.9866   $235.99   $236.00   $236.00  
  Purchase #3 $43.88   10.156%   $48.3365   $48.34   $48.35   $48.30  
  Purchase #4 $78.86   7.741%   $84.9646   $84.96   $84.95   $85.00  
  Purchase #5 $69.31   11.338%   $77.1684   $77.17   $77.15   $77.20  
  Purchase #6 $231.76   12.267%   $260.19   $260.19   $260.20   $260.20  
  Purchase #7 $65.92   13.665%   $74.928   $74.93   $74.95   $74.90  
  7 purchase totals = $774.52       $849.8513   $849.86   $849.90   $849.90