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 $113.77   5.144%   $119.6223   $119.62   $119.60   $119.60  
  Purchase #2 $214.28   4.696%   $224.3426   $224.34   $224.35   $224.30  
  Purchase #3 $124.92   6.767%   $133.3733   $133.37   $133.35   $133.40  
  Purchase #4 $93.38   12.208%   $104.7798   $104.78   $104.80   $104.80  
  Purchase #5 $239.60   8.745%   $260.553   $260.55   $260.55   $260.60  
  Purchase #6 $139.83   11.167%   $155.4448   $155.44   $155.45   $155.40  
  Purchase #7 $63.88   8.398%   $69.2446   $69.24   $69.25   $69.20  
  7 purchase totals = $989.66       $1,067.3604   $1,067.34   $1,067.35   $1,067.30