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 $250.66   10.385%   $276.691   $276.69   $276.70   $276.70  
  Purchase #2 $46.54   5.831%   $49.2537   $49.25   $49.25   $49.30  
  Purchase #3 $217.90   8.285%   $235.953   $235.95   $235.95   $236.00  
  Purchase #4 $9.94   6.783%   $10.6142   $10.61   $10.60   $10.60  
  Purchase #5 $236.98   11.693%   $264.6901   $264.69   $264.70   $264.70  
  Purchase #6 $212.26   13.563%   $241.0488   $241.05   $241.05   $241.00  
  Purchase #7 $248.69   10.502%   $274.8074   $274.81   $274.80   $274.80  
  7 purchase totals = $1,222.97       $1,353.0582   $1,353.05   $1,353.05   $1,353.10