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 $58.93   4.604%   $61.6431   $61.64   $61.65   $61.60  
  Purchase #2 $149.57   10.157%   $164.7618   $164.76   $164.75   $164.80  
  Purchase #3 $194.35   12.215%   $218.0899   $218.09   $218.10   $218.10  
  Purchase #4 $64.93   13.178%   $73.4865   $73.49   $73.50   $73.50  
  Purchase #5 $9.59   5.194%   $10.0881   $10.09   $10.10   $10.10  
  Purchase #6 $45.39   8.118%   $49.0748   $49.07   $49.05   $49.10  
  Purchase #7 $125.44   4.825%   $131.4925   $131.49   $131.50   $131.50  
  7 purchase totals = $648.20       $708.6367   $708.63   $708.65   $708.70