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 $127.99   3.329%   $132.2508   $132.25   $132.25   $132.30  
  Purchase #2 $71.81   6.686%   $76.6112   $76.61   $76.60   $76.60  
  Purchase #3 $47.73   6.786%   $50.969   $50.97   $50.95   $51.00  
  Purchase #4 $236.66   6.871%   $252.9209   $252.92   $252.90   $252.90  
  Purchase #5 $169.51   7.787%   $182.7097   $182.71   $182.70   $182.70  
  Purchase #6 $83.60   5.656%   $88.3284   $88.33   $88.35   $88.30  
  Purchase #7 $226.93   9.662%   $248.856   $248.86   $248.85   $248.90  
  7 purchase totals = $964.23       $1,032.6460   $1,032.65   $1,032.60   $1,032.70