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 $78.54   5.243%   $82.6579   $82.66   $82.65   $82.70  
  Purchase #2 $223.63   7.755%   $240.9725   $240.97   $240.95   $241.00  
  Purchase #3 $58.35   4.779%   $61.1385   $61.14   $61.15   $61.10  
  Purchase #4 $149.82   8.448%   $162.4768   $162.48   $162.50   $162.50  
  Purchase #5 $223.63   6.277%   $237.6673   $237.67   $237.65   $237.70  
  Purchase #6 $13.72   12.353%   $15.4148   $15.41   $15.40   $15.40  
  Purchase #7 $47.97   12.474%   $53.9538   $53.95   $53.95   $54.00  
  7 purchase totals = $795.66       $854.2816   $854.28   $854.25   $854.40