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 $99.33   5.377%   $104.671   $104.67   $104.65   $104.70  
  Purchase #2 $32.86   5.525%   $34.6755   $34.68   $34.70   $34.70  
  Purchase #3 $23.32   11.692%   $26.0466   $26.05   $26.05   $26.00  
  Purchase #4 $141.70   10.382%   $156.4113   $156.41   $156.40   $156.40  
  Purchase #5 $62.37   8.356%   $67.5816   $67.58   $67.60   $67.60  
  Purchase #6 $72.53   5.469%   $76.4967   $76.50   $76.50   $76.50  
  Purchase #7 $237.56   10.747%   $263.0906   $263.09   $263.10   $263.10  
  7 purchase totals = $669.67       $728.9733   $728.98   $729.00   $729.00