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 $239.95   11.359%   $267.2059   $267.21   $267.20   $267.20  
  Purchase #2 $236.35   12.824%   $266.6595   $266.66   $266.65   $266.70  
  Purchase #3 $41.39   12.801%   $46.6883   $46.69   $46.70   $46.70  
  Purchase #4 $242.55   12.720%   $273.4024   $273.40   $273.40   $273.40  
  Purchase #5 $204.56   3.153%   $211.0098   $211.01   $211.00   $211.00  
  Purchase #6 $26.76   7.342%   $28.7247   $28.72   $28.70   $28.70  
  Purchase #7 $37.60   5.348%   $39.6108   $39.61   $39.60   $39.60  
  7 purchase totals = $1,029.16       $1,133.3014   $1,133.30   $1,133.25   $1,133.30