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 $135.54   12.189%   $152.061   $152.06   $152.05   $152.10  
  Purchase #2 $68.38   7.353%   $73.408   $73.41   $73.40   $73.40  
  Purchase #3 $129.89   8.137%   $140.4591   $140.46   $140.45   $140.50  
  Purchase #4 $243.53   12.716%   $274.4973   $274.50   $274.50   $274.50  
  Purchase #5 $225.55   4.611%   $235.9501   $235.95   $235.95   $236.00  
  Purchase #6 $116.40   8.724%   $126.5547   $126.55   $126.55   $126.60  
  Purchase #7 $230.25   13.125%   $260.4703   $260.47   $260.45   $260.50  
  7 purchase totals = $1,149.54       $1,263.4005   $1,263.40   $1,263.35   $1,263.60