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 $50.48   11.659%   $56.3655   $56.37   $56.35   $56.40  
  Purchase #2 $58.31   4.706%   $61.0541   $61.05   $61.05   $61.10  
  Purchase #3 $86.76   8.491%   $94.1268   $94.13   $94.15   $94.10  
  Purchase #4 $241.49   3.817%   $250.7077   $250.71   $250.70   $250.70  
  Purchase #5 $235.45   4.803%   $246.7587   $246.76   $246.75   $246.80  
  Purchase #6 $235.40   13.802%   $267.8899   $267.89   $267.90   $267.90  
  Purchase #7 $52.56   6.191%   $55.814   $55.81   $55.80   $55.80  
  7 purchase totals = $960.45       $1,032.7167   $1,032.72   $1,032.70   $1,032.80