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 $90.71   11.596%   $101.2287   $101.23   $101.25   $101.20  
  Purchase #2 $236.92   13.798%   $269.6102   $269.61   $269.60   $269.60  
  Purchase #3 $151.29   10.219%   $166.7503   $166.75   $166.75   $166.80  
  Purchase #4 $9.81   13.664%   $11.1504   $11.15   $11.15   $11.20  
  Purchase #5 $95.64   12.396%   $107.4955   $107.50   $107.50   $107.50  
  Purchase #6 $49.52   13.651%   $56.28   $56.28   $56.30   $56.30  
  Purchase #7 $108.64   5.208%   $114.298   $114.30   $114.30   $114.30  
  7 purchase totals = $742.53       $826.8131   $826.82   $826.85   $826.90