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 $69.29   10.326%   $76.4449   $76.44   $76.45   $76.40  
  Purchase #2 $104.64   8.841%   $113.8912   $113.89   $113.90   $113.90  
  Purchase #3 $109.62   4.816%   $114.8993   $114.90   $114.90   $114.90  
  Purchase #4 $124.49   10.361%   $137.3884   $137.39   $137.40   $137.40  
  Purchase #5 $67.95   11.870%   $76.0157   $76.02   $76.00   $76.00  
  Purchase #6 $212.60   12.611%   $239.411   $239.41   $239.40   $239.40  
  Purchase #7 $11.62   8.674%   $12.6279   $12.63   $12.65   $12.60  
  7 purchase totals = $700.21       $770.6784   $770.68   $770.70   $770.60