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 $136.63   11.467%   $152.2974   $152.30   $152.30   $152.30  
  Purchase #2 $198.27   5.266%   $208.7109   $208.71   $208.70   $208.70  
  Purchase #3 $195.55   6.403%   $208.0711   $208.07   $208.05   $208.10  
  Purchase #4 $141.86   13.839%   $161.492   $161.49   $161.50   $161.50  
  Purchase #5 $166.25   4.802%   $174.2333   $174.23   $174.25   $174.20  
  Purchase #6 $202.57   5.720%   $214.157   $214.16   $214.15   $214.20  
  Purchase #7 $202.45   5.243%   $213.0645   $213.06   $213.05   $213.10  
  7 purchase totals = $1,243.58       $1,332.0262   $1,332.02   $1,332.00   $1,332.10