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 $57.83   11.718%   $64.6065   $64.61   $64.60   $64.60  
  Purchase #2 $237.98   9.527%   $260.6524   $260.65   $260.65   $260.70  
  Purchase #3 $250.89   13.121%   $283.8093   $283.81   $283.80   $283.80  
  Purchase #4 $81.89   5.828%   $86.6625   $86.66   $86.65   $86.70  
  Purchase #5 $63.67   5.313%   $67.0528   $67.05   $67.05   $67.10  
  Purchase #6 $60.97   11.356%   $67.8938   $67.89   $67.90   $67.90  
  Purchase #7 $42.77   8.862%   $46.5603   $46.56   $46.55   $46.60  
  7 purchase totals = $796.00       $877.2376   $877.23   $877.20   $877.40