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 $246.92   7.605%   $265.6983   $265.70   $265.70   $265.70  
  Purchase #2 $235.39   4.482%   $245.9402   $245.94   $245.95   $245.90  
  Purchase #3 $218.71   6.697%   $233.357   $233.36   $233.35   $233.40  
  Purchase #4 $76.64   10.747%   $84.8765   $84.88   $84.90   $84.90  
  Purchase #5 $183.38   8.295%   $198.5914   $198.59   $198.60   $198.60  
  Purchase #6 $146.68   5.470%   $154.7034   $154.70   $154.70   $154.70  
  Purchase #7 $224.99   9.495%   $246.3528   $246.35   $246.35   $246.40  
  7 purchase totals = $1,332.71       $1,429.5196   $1,429.52   $1,429.55   $1,429.60