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 $76.68   11.439%   $85.4514   $85.45   $85.45   $85.50  
  Purchase #2 $9.54   8.757%   $10.3754   $10.38   $10.40   $10.40  
  Purchase #3 $50.92   4.229%   $53.0734   $53.07   $53.05   $53.10  
  Purchase #4 $217.57   4.181%   $226.6666   $226.67   $226.65   $226.70  
  Purchase #5 $107.45   9.791%   $117.9704   $117.97   $117.95   $118.00  
  Purchase #6 $67.37   12.789%   $75.9859   $75.99   $76.00   $76.00  
  Purchase #7 $180.90   4.330%   $188.733   $188.73   $188.75   $188.70  
  7 purchase totals = $710.43       $758.2561   $758.26   $758.25   $758.40