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 $213.70   8.475%   $231.8111   $231.81   $231.80   $231.80  
  Purchase #2 $169.36   13.572%   $192.3455   $192.35   $192.35   $192.30  
  Purchase #3 $10.68   11.687%   $11.9282   $11.93   $11.95   $11.90  
  Purchase #4 $233.45   13.803%   $265.6731   $265.67   $265.65   $265.70  
  Purchase #5 $203.42   5.648%   $214.9092   $214.91   $214.90   $214.90  
  Purchase #6 $198.44   5.260%   $208.8779   $208.88   $208.90   $208.90  
  Purchase #7 $36.25   12.322%   $40.7167   $40.72   $40.70   $40.70  
  7 purchase totals = $1,065.30       $1,166.2617   $1,166.27   $1,166.25   $1,166.20