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 $248.40   5.543%   $262.1688   $262.17   $262.15   $262.20  
  Purchase #2 $187.51   7.460%   $201.4982   $201.50   $201.50   $201.50  
  Purchase #3 $124.39   11.423%   $138.5991   $138.60   $138.60   $138.60  
  Purchase #4 $43.84   8.108%   $47.3945   $47.39   $47.40   $47.40  
  Purchase #5 $58.94   4.577%   $61.6377   $61.64   $61.65   $61.60  
  Purchase #6 $245.41   5.856%   $259.7812   $259.78   $259.80   $259.80  
  Purchase #7 $56.30   6.725%   $60.0862   $60.09   $60.10   $60.10  
  7 purchase totals = $964.79       $1,031.1657   $1,031.17   $1,031.20   $1,031.20