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 $55.54   8.571%   $60.3003   $60.30   $60.30   $60.30  
  Purchase #2 $207.48   10.724%   $229.7302   $229.73   $229.75   $229.70  
  Purchase #3 $164.80   7.512%   $177.1798   $177.18   $177.20   $177.20  
  Purchase #4 $67.76   10.238%   $74.6973   $74.70   $74.70   $74.70  
  Purchase #5 $79.34   3.479%   $82.1002   $82.10   $82.10   $82.10  
  Purchase #6 $94.60   3.834%   $98.227   $98.23   $98.25   $98.20  
  Purchase #7 $204.55   10.187%   $225.3875   $225.39   $225.40   $225.40  
  7 purchase totals = $874.07       $947.6223   $947.63   $947.70   $947.60