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 $110.31   11.694%   $123.2097   $123.21   $123.20   $123.20  
  Purchase #2 $248.76   5.190%   $261.6706   $261.67   $261.65   $261.70  
  Purchase #3 $226.37   11.459%   $252.3097   $252.31   $252.30   $252.30  
  Purchase #4 $8.72   12.794%   $9.8356   $9.84   $9.85   $9.80  
  Purchase #5 $24.40   9.262%   $26.6599   $26.66   $26.65   $26.70  
  Purchase #6 $170.95   13.222%   $193.553   $193.55   $193.55   $193.60  
  Purchase #7 $211.65   12.103%   $237.266   $237.27   $237.25   $237.30  
  7 purchase totals = $1,001.16       $1,104.5045   $1,104.51   $1,104.45   $1,104.60