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 $52.81   3.663%   $54.7444   $54.74   $54.75   $54.70  
  Purchase #2 $73.62   4.195%   $76.7084   $76.71   $76.70   $76.70  
  Purchase #3 $62.29   5.458%   $65.6898   $65.69   $65.70   $65.70  
  Purchase #4 $17.86   4.546%   $18.6719   $18.67   $18.65   $18.70  
  Purchase #5 $203.69   3.549%   $210.919   $210.92   $210.90   $210.90  
  Purchase #6 $34.69   5.833%   $36.7135   $36.71   $36.70   $36.70  
  Purchase #7 $208.62   13.738%   $237.2802   $237.28   $237.30   $237.30  
  7 purchase totals = $653.58       $700.7272   $700.72   $700.70   $700.70