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 $83.98   11.626%   $93.7435   $93.74   $93.75   $93.70  
  Purchase #2 $24.46   8.517%   $26.5433   $26.54   $26.55   $26.50  
  Purchase #3 $165.26   6.628%   $176.2134   $176.21   $176.20   $176.20  
  Purchase #4 $178.33   6.670%   $190.2246   $190.22   $190.20   $190.20  
  Purchase #5 $26.97   13.566%   $30.6288   $30.63   $30.65   $30.60  
  Purchase #6 $101.61   11.662%   $113.4598   $113.46   $113.45   $113.50  
  Purchase #7 $177.45   10.283%   $195.6972   $195.70   $195.70   $195.70  
  7 purchase totals = $758.06       $826.5106   $826.50   $826.50   $826.40