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 $71.63   4.141%   $74.5962   $74.60   $74.60   $74.60  
  Purchase #2 $65.28   13.734%   $74.2456   $74.25   $74.25   $74.20  
  Purchase #3 $239.89   10.656%   $265.4527   $265.45   $265.45   $265.50  
  Purchase #4 $190.97   5.646%   $201.7522   $201.75   $201.75   $201.80  
  Purchase #5 $70.54   4.447%   $73.6769   $73.68   $73.70   $73.70  
  Purchase #6 $71.66   13.797%   $81.5469   $81.55   $81.55   $81.50  
  Purchase #7 $210.61   9.241%   $230.0725   $230.07   $230.05   $230.10  
  7 purchase totals = $920.58       $1,001.3430   $1,001.35   $1,001.35   $1,001.40