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 $210.83   4.545%   $220.4122   $220.41   $220.40   $220.40  
  Purchase #2 $40.33   6.469%   $42.9389   $42.94   $42.95   $42.90  
  Purchase #3 $192.46   8.395%   $208.617   $208.62   $208.60   $208.60  
  Purchase #4 $134.26   9.182%   $146.5878   $146.59   $146.60   $146.60  
  Purchase #5 $110.81   10.320%   $122.2456   $122.25   $122.25   $122.20  
  Purchase #6 $71.43   7.675%   $76.9123   $76.91   $76.90   $76.90  
  Purchase #7 $63.92   13.192%   $72.3523   $72.35   $72.35   $72.40  
  7 purchase totals = $824.04       $890.0661   $890.07   $890.05   $890.00