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 $205.49   10.285%   $226.6246   $226.62   $226.60   $226.60  
  Purchase #2 $17.58   11.219%   $19.5523   $19.55   $19.55   $19.60  
  Purchase #3 $158.32   7.416%   $170.061   $170.06   $170.05   $170.10  
  Purchase #4 $134.73   7.343%   $144.6232   $144.62   $144.60   $144.60  
  Purchase #5 $195.75   9.328%   $214.0096   $214.01   $214.00   $214.00  
  Purchase #6 $242.65   3.855%   $252.0042   $252.00   $252.00   $252.00  
  Purchase #7 $163.57   6.680%   $174.4965   $174.50   $174.50   $174.50  
  7 purchase totals = $1,118.09       $1,201.3714   $1,201.36   $1,201.30   $1,201.40