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 $25.46   3.317%   $26.3045   $26.30   $26.30   $26.30  
  Purchase #2 $215.70   10.520%   $238.3916   $238.39   $238.40   $238.40  
  Purchase #3 $46.63   6.712%   $49.7598   $49.76   $49.75   $49.80  
  Purchase #4 $248.81   5.194%   $261.7332   $261.73   $261.75   $261.70  
  Purchase #5 $214.81   8.651%   $233.3932   $233.39   $233.40   $233.40  
  Purchase #6 $202.56   13.473%   $229.8509   $229.85   $229.85   $229.90  
  Purchase #7 $238.67   10.243%   $263.117   $263.12   $263.10   $263.10  
  7 purchase totals = $1,192.64       $1,302.5502   $1,302.54   $1,302.55   $1,302.60