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 $68.29   8.343%   $73.9874   $73.99   $74.00   $74.00  
  Purchase #2 $163.83   4.156%   $170.6388   $170.64   $170.65   $170.60  
  Purchase #3 $240.58   8.763%   $261.662   $261.66   $261.65   $261.70  
  Purchase #4 $102.75   9.625%   $112.6397   $112.64   $112.65   $112.60  
  Purchase #5 $115.34   6.281%   $122.5845   $122.58   $122.60   $122.60  
  Purchase #6 $27.88   9.760%   $30.6011   $30.60   $30.60   $30.60  
  Purchase #7 $206.75   8.680%   $224.6959   $224.70   $224.70   $224.70  
  7 purchase totals = $925.42       $996.8094   $996.81   $996.85   $996.80