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 $213.52   13.689%   $242.7488   $242.75   $242.75   $242.70  
  Purchase #2 $69.65   5.638%   $73.5769   $73.58   $73.60   $73.60  
  Purchase #3 $81.69   6.601%   $87.0824   $87.08   $87.10   $87.10  
  Purchase #4 $152.64   5.157%   $160.5116   $160.51   $160.50   $160.50  
  Purchase #5 $134.60   9.169%   $146.9415   $146.94   $146.95   $146.90  
  Purchase #6 $78.59   3.231%   $81.1292   $81.13   $81.15   $81.10  
  Purchase #7 $104.54   9.671%   $114.6501   $114.65   $114.65   $114.70  
  7 purchase totals = $835.23       $906.6405   $906.64   $906.70   $906.60