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 $131.84   7.350%   $141.5302   $141.53   $141.55   $141.50  
  Purchase #2 $218.81   7.260%   $234.6956   $234.70   $234.70   $234.70  
  Purchase #3 $20.25   13.259%   $22.9349   $22.93   $22.95   $22.90  
  Purchase #4 $47.66   7.812%   $51.3832   $51.38   $51.40   $51.40  
  Purchase #5 $196.97   6.243%   $209.2668   $209.27   $209.25   $209.30  
  Purchase #6 $159.38   3.358%   $164.732   $164.73   $164.75   $164.70  
  Purchase #7 $76.46   4.639%   $80.007   $80.01   $80.00   $80.00  
  7 purchase totals = $851.37       $904.5497   $904.55   $904.60   $904.50