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 $195.53   6.621%   $208.476   $208.48   $208.50   $208.50  
  Purchase #2 $209.71   7.866%   $226.2058   $226.21   $226.20   $226.20  
  Purchase #3 $38.63   10.873%   $42.8302   $42.83   $42.85   $42.80  
  Purchase #4 $156.99   8.209%   $169.8773   $169.88   $169.90   $169.90  
  Purchase #5 $104.88   3.421%   $108.4679   $108.47   $108.45   $108.50  
  Purchase #6 $212.76   13.708%   $241.9251   $241.93   $241.95   $241.90  
  Purchase #7 $58.73   6.330%   $62.4476   $62.45   $62.45   $62.40  
  7 purchase totals = $977.23       $1,060.2299   $1,060.25   $1,060.30   $1,060.20