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 $61.63   13.357%   $69.8619   $69.86   $69.85   $69.90  
  Purchase #2 $72.91   4.837%   $76.4367   $76.44   $76.45   $76.40  
  Purchase #3 $103.26   10.869%   $114.4833   $114.48   $114.50   $114.50  
  Purchase #4 $206.90   13.682%   $235.2081   $235.21   $235.20   $235.20  
  Purchase #5 $146.71   13.604%   $166.6684   $166.67   $166.65   $166.70  
  Purchase #6 $6.32   9.109%   $6.8957   $6.90   $6.90   $6.90  
  Purchase #7 $80.40   6.357%   $85.511   $85.51   $85.50   $85.50  
  7 purchase totals = $678.13       $755.0651   $755.07   $755.05   $755.10