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 $67.46   13.219%   $76.3775   $76.38   $76.40   $76.40  
  Purchase #2 $98.83   4.497%   $103.2744   $103.27   $103.25   $103.30  
  Purchase #3 $60.31   7.166%   $64.6318   $64.63   $64.65   $64.60  
  Purchase #4 $92.61   6.423%   $98.5583   $98.56   $98.55   $98.60  
  Purchase #5 $164.63   9.420%   $180.1381   $180.14   $180.15   $180.10  
  Purchase #6 $201.39   8.329%   $218.1638   $218.16   $218.15   $218.20  
  Purchase #7 $224.25   7.788%   $241.7146   $241.71   $241.70   $241.70  
  7 purchase totals = $909.48       $982.8585   $982.85   $982.85   $982.90