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 $63.36   3.667%   $65.6834   $65.68   $65.70   $65.70  
  Purchase #2 $133.59   7.824%   $144.0421   $144.04   $144.05   $144.00  
  Purchase #3 $191.65   3.497%   $198.352   $198.35   $198.35   $198.40  
  Purchase #4 $140.73   3.295%   $145.3671   $145.37   $145.35   $145.40  
  Purchase #5 $116.63   3.481%   $120.6899   $120.69   $120.70   $120.70  
  Purchase #6 $177.53   5.256%   $186.861   $186.86   $186.85   $186.90  
  Purchase #7 $9.91   11.225%   $11.0224   $11.02   $11.00   $11.00  
  7 purchase totals = $833.40       $872.0179   $872.01   $872.00   $872.10