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 $214.81   8.776%   $233.6617   $233.66   $233.65   $233.70  
  Purchase #2 $198.87   4.299%   $207.4194   $207.42   $207.40   $207.40  
  Purchase #3 $170.86   8.358%   $185.1405   $185.14   $185.15   $185.10  
  Purchase #4 $100.54   7.773%   $108.355   $108.36   $108.35   $108.40  
  Purchase #5 $156.86   12.617%   $176.651   $176.65   $176.65   $176.70  
  Purchase #6 $27.85   5.561%   $29.3987   $29.40   $29.40   $29.40  
  Purchase #7 $32.87   8.158%   $35.5515   $35.55   $35.55   $35.60  
  7 purchase totals = $902.66       $976.1778   $976.18   $976.15   $976.30