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 $101.54   13.207%   $114.9504   $114.95   $114.95   $115.00  
  Purchase #2 $142.32   10.454%   $157.1981   $157.20   $157.20   $157.20  
  Purchase #3 $148.31   12.357%   $166.6367   $166.64   $166.65   $166.60  
  Purchase #4 $85.65   8.728%   $93.1255   $93.13   $93.15   $93.10  
  Purchase #5 $56.95   11.849%   $63.698   $63.70   $63.70   $63.70  
  Purchase #6 $34.26   5.414%   $36.1148   $36.11   $36.10   $36.10  
  Purchase #7 $60.92   6.441%   $64.8439   $64.84   $64.85   $64.80  
  7 purchase totals = $629.95       $696.5674   $696.57   $696.60   $696.50