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 $49.26   11.464%   $54.9072   $54.91   $54.90   $54.90  
  Purchase #2 $113.70   4.628%   $118.962   $118.96   $118.95   $119.00  
  Purchase #3 $144.81   6.843%   $154.7193   $154.72   $154.70   $154.70  
  Purchase #4 $155.38   5.555%   $164.0114   $164.01   $164.00   $164.00  
  Purchase #5 $170.97   4.632%   $178.8893   $178.89   $178.90   $178.90  
  Purchase #6 $65.47   13.105%   $74.0498   $74.05   $74.05   $74.00  
  Purchase #7 $201.76   12.508%   $226.9961   $227.00   $227.00   $227.00  
  7 purchase totals = $901.35       $972.5351   $972.54   $972.50   $972.50