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 $236.53   6.868%   $252.7749   $252.77   $252.75   $252.80  
  Purchase #2 $216.48   10.835%   $239.9356   $239.94   $239.95   $239.90  
  Purchase #3 $18.54   7.292%   $19.8919   $19.89   $19.90   $19.90  
  Purchase #4 $174.90   3.418%   $180.8781   $180.88   $180.90   $180.90  
  Purchase #5 $183.54   12.391%   $206.2824   $206.28   $206.30   $206.30  
  Purchase #6 $107.72   6.395%   $114.6087   $114.61   $114.60   $114.60  
  Purchase #7 $188.48   3.340%   $194.7752   $194.78   $194.80   $194.80  
  7 purchase totals = $1,126.19       $1,209.1468   $1,209.15   $1,209.20   $1,209.20