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 $55.42   11.678%   $61.8919   $61.89   $61.90   $61.90  
  Purchase #2 $151.94   5.319%   $160.0217   $160.02   $160.00   $160.00  
  Purchase #3 $114.71   6.209%   $121.8323   $121.83   $121.85   $121.80  
  Purchase #4 $32.62   12.180%   $36.5931   $36.59   $36.60   $36.60  
  Purchase #5 $66.77   9.821%   $73.3275   $73.33   $73.35   $73.30  
  Purchase #6 $107.89   13.622%   $122.5868   $122.59   $122.60   $122.60  
  Purchase #7 $136.86   3.448%   $141.5789   $141.58   $141.60   $141.60  
  7 purchase totals = $666.21       $717.8322   $717.83   $717.90   $717.80