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 $63.27   4.400%   $66.0539   $66.05   $66.05   $66.10  
  Purchase #2 $179.95   7.455%   $193.3653   $193.37   $193.35   $193.40  
  Purchase #3 $18.39   4.610%   $19.2378   $19.24   $19.25   $19.20  
  Purchase #4 $40.71   5.747%   $43.0496   $43.05   $43.05   $43.00  
  Purchase #5 $95.82   8.747%   $104.2014   $104.20   $104.20   $104.20  
  Purchase #6 $90.83   3.440%   $93.9546   $93.95   $93.95   $94.00  
  Purchase #7 $231.35   7.442%   $248.5671   $248.57   $248.55   $248.60  
  7 purchase totals = $720.32       $768.4297   $768.43   $768.40   $768.50