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 $234.27   10.611%   $259.1284   $259.13   $259.15   $259.10  
  Purchase #2 $71.76   8.432%   $77.8108   $77.81   $77.80   $77.80  
  Purchase #3 $15.92   8.769%   $17.316   $17.32   $17.30   $17.30  
  Purchase #4 $178.45   6.849%   $190.672   $190.67   $190.65   $190.70  
  Purchase #5 $102.37   6.173%   $108.6893   $108.69   $108.70   $108.70  
  Purchase #6 $138.28   13.242%   $156.591   $156.59   $156.60   $156.60  
  Purchase #7 $190.51   8.552%   $206.8024   $206.80   $206.80   $206.80  
  7 purchase totals = $931.56       $1,017.0099   $1,017.01   $1,017.00   $1,017.00