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 $228.87   13.175%   $259.0236   $259.02   $259.00   $259.00  
  Purchase #2 $82.92   8.775%   $90.1962   $90.20   $90.20   $90.20  
  Purchase #3 $177.71   13.826%   $202.2802   $202.28   $202.30   $202.30  
  Purchase #4 $236.36   13.841%   $269.0746   $269.07   $269.05   $269.10  
  Purchase #5 $206.94   3.194%   $213.5497   $213.55   $213.55   $213.50  
  Purchase #6 $115.25   6.186%   $122.3794   $122.38   $122.40   $122.40  
  Purchase #7 $89.71   6.789%   $95.8004   $95.80   $95.80   $95.80  
  7 purchase totals = $1,137.76       $1,252.3041   $1,252.30   $1,252.30   $1,252.30