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 $236.85   7.536%   $254.699   $254.70   $254.70   $254.70  
  Purchase #2 $56.62   3.171%   $58.4154   $58.42   $58.40   $58.40  
  Purchase #3 $55.37   11.267%   $61.6085   $61.61   $61.60   $61.60  
  Purchase #4 $139.72   5.122%   $146.8765   $146.88   $146.90   $146.90  
  Purchase #5 $109.49   7.196%   $117.3689   $117.37   $117.35   $117.40  
  Purchase #6 $223.30   4.522%   $233.3976   $233.40   $233.40   $233.40  
  Purchase #7 $142.97   9.196%   $156.1175   $156.12   $156.10   $156.10  
  7 purchase totals = $964.32       $1,028.4834   $1,028.50   $1,028.45   $1,028.50