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 $10.86   5.717%   $11.4809   $11.48   $11.50   $11.50  
  Purchase #2 $114.75   13.535%   $130.2814   $130.28   $130.30   $130.30  
  Purchase #3 $76.86   12.228%   $86.2584   $86.26   $86.25   $86.30  
  Purchase #4 $241.38   9.115%   $263.3818   $263.38   $263.40   $263.40  
  Purchase #5 $96.59   7.719%   $104.0458   $104.05   $104.05   $104.00  
  Purchase #6 $166.81   11.867%   $186.6053   $186.61   $186.60   $186.60  
  Purchase #7 $196.56   6.687%   $209.704   $209.70   $209.70   $209.70  
  7 purchase totals = $903.81       $991.7576   $991.76   $991.80   $991.80