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 $136.95   13.853%   $155.9217   $155.92   $155.90   $155.90  
  Purchase #2 $146.87   6.509%   $156.4298   $156.43   $156.45   $156.40  
  Purchase #3 $91.32   6.748%   $97.4823   $97.48   $97.50   $97.50  
  Purchase #4 $70.94   7.466%   $76.2364   $76.24   $76.25   $76.20  
  Purchase #5 $113.28   10.690%   $125.3896   $125.39   $125.40   $125.40  
  Purchase #6 $218.77   8.647%   $237.687   $237.69   $237.70   $237.70  
  Purchase #7 $236.36   10.321%   $260.7547   $260.75   $260.75   $260.80  
  7 purchase totals = $1,014.49       $1,109.9015   $1,109.90   $1,109.95   $1,109.90