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 $68.88   11.652%   $76.9059   $76.91   $76.90   $76.90  
  Purchase #2 $235.79   10.654%   $260.9111   $260.91   $260.90   $260.90  
  Purchase #3 $59.86   11.176%   $66.55   $66.55   $66.55   $66.60  
  Purchase #4 $104.42   3.800%   $108.388   $108.39   $108.40   $108.40  
  Purchase #5 $22.96   7.648%   $24.716   $24.72   $24.70   $24.70  
  Purchase #6 $129.56   4.131%   $134.9121   $134.91   $134.90   $134.90  
  Purchase #7 $13.83   4.627%   $14.4699   $14.47   $14.45   $14.50  
  7 purchase totals = $635.30       $686.8530   $686.86   $686.80   $686.90