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 $62.86   13.757%   $71.5077   $71.51   $71.50   $71.50  
  Purchase #2 $245.87   6.846%   $262.7023   $262.70   $262.70   $262.70  
  Purchase #3 $90.52   4.335%   $94.444   $94.44   $94.45   $94.40  
  Purchase #4 $171.48   6.502%   $182.6296   $182.63   $182.65   $182.60  
  Purchase #5 $76.75   5.765%   $81.1746   $81.17   $81.15   $81.20  
  Purchase #6 $140.91   6.563%   $150.1579   $150.16   $150.15   $150.20  
  Purchase #7 $167.82   6.502%   $178.7317   $178.73   $178.75   $178.70  
  7 purchase totals = $956.21       $1,021.3478   $1,021.34   $1,021.35   $1,021.30