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 $29.69   13.468%   $33.6886   $33.69   $33.70   $33.70  
  Purchase #2 $244.88   7.116%   $262.3057   $262.31   $262.30   $262.30  
  Purchase #3 $101.41   12.216%   $113.7982   $113.80   $113.80   $113.80  
  Purchase #4 $188.81   13.426%   $214.1596   $214.16   $214.15   $214.20  
  Purchase #5 $237.38   6.372%   $252.5059   $252.51   $252.50   $252.50  
  Purchase #6 $119.94   3.122%   $123.6845   $123.68   $123.70   $123.70  
  Purchase #7 $146.31   5.587%   $154.4843   $154.48   $154.50   $154.50  
  7 purchase totals = $1,068.42       $1,154.6268   $1,154.63   $1,154.65   $1,154.70