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 $213.46   13.213%   $241.6645   $241.66   $241.65   $241.70  
  Purchase #2 $176.92   12.126%   $198.3733   $198.37   $198.35   $198.40  
  Purchase #3 $124.89   5.392%   $131.6241   $131.62   $131.60   $131.60  
  Purchase #4 $25.80   8.591%   $28.0165   $28.02   $28.00   $28.00  
  Purchase #5 $115.27   4.221%   $120.1355   $120.14   $120.15   $120.10  
  Purchase #6 $52.37   13.578%   $59.4808   $59.48   $59.50   $59.50  
  Purchase #7 $128.99   8.860%   $140.4185   $140.42   $140.40   $140.40  
  7 purchase totals = $837.70       $919.7132   $919.71   $919.65   $919.70