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 $188.91   13.295%   $214.0256   $214.03   $214.05   $214.00  
  Purchase #2 $135.41   5.237%   $142.5014   $142.50   $142.50   $142.50  
  Purchase #3 $244.33   11.302%   $271.9442   $271.94   $271.95   $271.90  
  Purchase #4 $248.61   11.285%   $276.6656   $276.67   $276.65   $276.70  
  Purchase #5 $69.32   10.808%   $76.8121   $76.81   $76.80   $76.80  
  Purchase #6 $184.40   5.527%   $194.5918   $194.59   $194.60   $194.60  
  Purchase #7 $6.65   4.855%   $6.9729   $6.97   $6.95   $7.00  
  7 purchase totals = $1,077.63       $1,183.5136   $1,183.51   $1,183.50   $1,183.50