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 $68.99   10.738%   $76.3981   $76.40   $76.40   $76.40  
  Purchase #2 $216.50   8.659%   $235.2467   $235.25   $235.25   $235.20  
  Purchase #3 $133.59   3.683%   $138.5101   $138.51   $138.50   $138.50  
  Purchase #4 $146.83   12.821%   $165.6551   $165.66   $165.65   $165.70  
  Purchase #5 $82.27   12.603%   $92.6385   $92.64   $92.65   $92.60  
  Purchase #6 $205.88   13.503%   $233.68   $233.68   $233.70   $233.70  
  Purchase #7 $202.76   8.282%   $219.5526   $219.55   $219.55   $219.60  
  7 purchase totals = $1,056.82       $1,161.6811   $1,161.69   $1,161.70   $1,161.70