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 $59.61   13.334%   $67.5584   $67.56   $67.55   $67.60  
  Purchase #2 $118.88   5.834%   $125.8155   $125.82   $125.80   $125.80  
  Purchase #3 $40.48   7.236%   $43.4091   $43.41   $43.40   $43.40  
  Purchase #4 $250.46   7.126%   $268.3078   $268.31   $268.30   $268.30  
  Purchase #5 $70.40   10.622%   $77.8779   $77.88   $77.90   $77.90  
  Purchase #6 $49.62   13.433%   $56.2855   $56.29   $56.30   $56.30  
  Purchase #7 $247.25   10.182%   $272.425   $272.43   $272.45   $272.40  
  7 purchase totals = $836.70       $911.6792   $911.70   $911.70   $911.70