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 $240.49   11.760%   $268.7716   $268.77   $268.75   $268.80  
  Purchase #2 $173.78   4.298%   $181.2491   $181.25   $181.25   $181.20  
  Purchase #3 $175.29   4.719%   $183.5619   $183.56   $183.55   $183.60  
  Purchase #4 $18.47   12.617%   $20.8004   $20.80   $20.80   $20.80  
  Purchase #5 $219.71   12.627%   $247.4528   $247.45   $247.45   $247.50  
  Purchase #6 $94.88   10.577%   $104.9155   $104.92   $104.90   $104.90  
  Purchase #7 $206.92   11.512%   $230.7406   $230.74   $230.75   $230.70  
  7 purchase totals = $1,129.54       $1,237.4919   $1,237.49   $1,237.45   $1,237.50