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 $43.41   6.751%   $46.3406   $46.34   $46.35   $46.30  
  Purchase #2 $133.92   3.483%   $138.5844   $138.58   $138.60   $138.60  
  Purchase #3 $76.70   12.820%   $86.5329   $86.53   $86.55   $86.50  
  Purchase #4 $162.63   8.711%   $176.7967   $176.80   $176.80   $176.80  
  Purchase #5 $168.70   6.476%   $179.625   $179.63   $179.65   $179.60  
  Purchase #6 $180.44   12.619%   $203.2097   $203.21   $203.20   $203.20  
  Purchase #7 $169.69   9.383%   $185.612   $185.61   $185.60   $185.60  
  7 purchase totals = $935.49       $1,016.7013   $1,016.70   $1,016.75   $1,016.60