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 $216.92   11.576%   $242.0307   $242.03   $242.05   $242.00  
  Purchase #2 $132.64   8.286%   $143.6306   $143.63   $143.65   $143.60  
  Purchase #3 $249.72   3.730%   $259.0346   $259.03   $259.05   $259.00  
  Purchase #4 $124.32   13.217%   $140.7514   $140.75   $140.75   $140.80  
  Purchase #5 $83.31   10.818%   $92.3225   $92.32   $92.30   $92.30  
  Purchase #6 $132.36   5.803%   $140.0409   $140.04   $140.05   $140.00  
  Purchase #7 $197.70   5.284%   $208.1465   $208.15   $208.15   $208.10  
  7 purchase totals = $1,136.97       $1,225.9572   $1,225.95   $1,226.00   $1,225.80