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 $222.55   10.871%   $246.7434   $246.74   $246.75   $246.70  
  Purchase #2 $184.59   3.117%   $190.3437   $190.34   $190.35   $190.30  
  Purchase #3 $246.42   10.595%   $272.5282   $272.53   $272.55   $272.50  
  Purchase #4 $218.77   13.227%   $247.7067   $247.71   $247.70   $247.70  
  Purchase #5 $209.28   5.754%   $221.322   $221.32   $221.30   $221.30  
  Purchase #6 $66.74   3.660%   $69.1827   $69.18   $69.20   $69.20  
  Purchase #7 $102.31   11.587%   $114.1647   $114.16   $114.15   $114.20  
  7 purchase totals = $1,250.66       $1,361.9914   $1,361.98   $1,362.00   $1,361.90