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 $218.28   10.526%   $241.2562   $241.26   $241.25   $241.30  
  Purchase #2 $107.29   5.826%   $113.5407   $113.54   $113.55   $113.50  
  Purchase #3 $65.36   13.480%   $74.1705   $74.17   $74.15   $74.20  
  Purchase #4 $83.58   6.833%   $89.291   $89.29   $89.30   $89.30  
  Purchase #5 $205.84   4.184%   $214.4523   $214.45   $214.45   $214.50  
  Purchase #6 $183.68   13.637%   $208.7284   $208.73   $208.75   $208.70  
  Purchase #7 $231.90   11.473%   $258.5059   $258.51   $258.50   $258.50  
  7 purchase totals = $1,095.93       $1,199.9450   $1,199.95   $1,199.95   $1,200.00