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 $68.32   9.361%   $74.7154   $74.72   $74.70   $74.70  
  Purchase #2 $73.64   4.448%   $76.9155   $76.92   $76.90   $76.90  
  Purchase #3 $41.36   3.674%   $42.8796   $42.88   $42.90   $42.90  
  Purchase #4 $26.30   7.254%   $28.2078   $28.21   $28.20   $28.20  
  Purchase #5 $124.84   13.537%   $141.7396   $141.74   $141.75   $141.70  
  Purchase #6 $180.81   6.243%   $192.098   $192.10   $192.10   $192.10  
  Purchase #7 $196.26   6.163%   $208.3555   $208.36   $208.35   $208.40  
  7 purchase totals = $711.53       $764.9114   $764.93   $764.90   $764.90