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 $124.80   12.805%   $140.7806   $140.78   $140.80   $140.80  
  Purchase #2 $248.97   12.676%   $280.5294   $280.53   $280.55   $280.50  
  Purchase #3 $247.42   5.715%   $261.5601   $261.56   $261.55   $261.60  
  Purchase #4 $44.96   3.342%   $46.4626   $46.46   $46.45   $46.50  
  Purchase #5 $6.35   6.841%   $6.7844   $6.78   $6.80   $6.80  
  Purchase #6 $218.68   13.796%   $248.8491   $248.85   $248.85   $248.80  
  Purchase #7 $109.70   3.560%   $113.6053   $113.61   $113.60   $113.60  
  7 purchase totals = $1,000.88       $1,098.5715   $1,098.57   $1,098.60   $1,098.60