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 $23.37   6.701%   $24.936   $24.94   $24.95   $24.90  
  Purchase #2 $67.99   12.475%   $76.4718   $76.47   $76.45   $76.50  
  Purchase #3 $154.86   13.396%   $175.605   $175.61   $175.60   $175.60  
  Purchase #4 $63.63   8.827%   $69.2466   $69.25   $69.25   $69.20  
  Purchase #5 $130.97   3.556%   $135.6273   $135.63   $135.65   $135.60  
  Purchase #6 $223.63   4.815%   $234.3978   $234.40   $234.40   $234.40  
  Purchase #7 $45.35   6.570%   $48.3295   $48.33   $48.35   $48.30  
  7 purchase totals = $709.80       $764.6140   $764.63   $764.65   $764.50