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 $61.32   13.268%   $69.4559   $69.46   $69.45   $69.50  
  Purchase #2 $75.36   9.166%   $82.2675   $82.27   $82.25   $82.30  
  Purchase #3 $98.45   9.256%   $107.5625   $107.56   $107.55   $107.60  
  Purchase #4 $100.32   3.296%   $103.6265   $103.63   $103.65   $103.60  
  Purchase #5 $70.90   4.499%   $74.0898   $74.09   $74.10   $74.10  
  Purchase #6 $151.46   8.371%   $164.1387   $164.14   $164.15   $164.10  
  Purchase #7 $244.37   10.757%   $270.6569   $270.66   $270.65   $270.70  
  7 purchase totals = $802.18       $871.7978   $871.81   $871.80   $871.90