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 $117.64   12.164%   $131.9497   $131.95   $131.95   $131.90  
  Purchase #2 $124.35   10.335%   $137.2016   $137.20   $137.20   $137.20  
  Purchase #3 $117.98   12.423%   $132.6367   $132.64   $132.65   $132.60  
  Purchase #4 $202.99   9.662%   $222.6029   $222.60   $222.60   $222.60  
  Purchase #5 $158.42   5.255%   $166.745   $166.75   $166.75   $166.70  
  Purchase #6 $184.80   11.289%   $205.6621   $205.66   $205.65   $205.70  
  Purchase #7 $21.85   9.354%   $23.8938   $23.89   $23.90   $23.90  
  7 purchase totals = $928.03       $1,020.6918   $1,020.69   $1,020.70   $1,020.60