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 $175.71   3.660%   $182.141   $182.14   $182.15   $182.10  
  Purchase #2 $241.78   3.788%   $250.9386   $250.94   $250.95   $250.90  
  Purchase #3 $57.94   5.755%   $61.2744   $61.27   $61.25   $61.30  
  Purchase #4 $39.38   7.685%   $42.4064   $42.41   $42.40   $42.40  
  Purchase #5 $163.88   11.837%   $183.2785   $183.28   $183.30   $183.30  
  Purchase #6 $202.92   6.710%   $216.5359   $216.54   $216.55   $216.50  
  Purchase #7 $237.62   12.753%   $267.9237   $267.92   $267.90   $267.90  
  7 purchase totals = $1,119.23       $1,204.4985   $1,204.50   $1,204.50   $1,204.40