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 $235.28   11.150%   $261.5137   $261.51   $261.50   $261.50  
  Purchase #2 $71.31   3.215%   $73.6026   $73.60   $73.60   $73.60  
  Purchase #3 $25.63   3.860%   $26.6193   $26.62   $26.60   $26.60  
  Purchase #4 $191.92   5.586%   $202.6407   $202.64   $202.65   $202.60  
  Purchase #5 $195.35   10.747%   $216.3443   $216.34   $216.35   $216.30  
  Purchase #6 $130.58   8.328%   $141.4547   $141.45   $141.45   $141.50  
  Purchase #7 $47.88   3.419%   $49.517   $49.52   $49.50   $49.50  
  7 purchase totals = $897.95       $971.6923   $971.68   $971.65   $971.60