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 $192.51   11.697%   $215.0279   $215.03   $215.05   $215.00  
  Purchase #2 $81.66   6.119%   $86.6568   $86.66   $86.65   $86.70  
  Purchase #3 $121.30   12.357%   $136.289   $136.29   $136.30   $136.30  
  Purchase #4 $235.83   10.225%   $259.9436   $259.94   $259.95   $259.90  
  Purchase #5 $211.37   9.170%   $230.7526   $230.75   $230.75   $230.80  
  Purchase #6 $215.75   9.837%   $236.9733   $236.97   $236.95   $237.00  
  Purchase #7 $248.80   3.592%   $257.7369   $257.74   $257.75   $257.70  
  7 purchase totals = $1,307.22       $1,423.3801   $1,423.38   $1,423.40   $1,423.40