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 $61.31   6.585%   $65.3473   $65.35   $65.35   $65.30  
  Purchase #2 $174.76   13.677%   $198.6619   $198.66   $198.65   $198.70  
  Purchase #3 $26.34   3.508%   $27.264   $27.26   $27.25   $27.30  
  Purchase #4 $216.63   6.716%   $231.1789   $231.18   $231.20   $231.20  
  Purchase #5 $24.97   7.714%   $26.8962   $26.90   $26.90   $26.90  
  Purchase #6 $121.64   6.404%   $129.4298   $129.43   $129.45   $129.40  
  Purchase #7 $202.49   7.616%   $217.9116   $217.91   $217.90   $217.90  
  7 purchase totals = $828.14       $896.6897   $896.69   $896.70   $896.70