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 $237.62   13.519%   $269.7438   $269.74   $269.75   $269.70  
  Purchase #2 $198.99   11.210%   $221.2968   $221.30   $221.30   $221.30  
  Purchase #3 $86.31   10.325%   $95.2215   $95.22   $95.20   $95.20  
  Purchase #4 $249.50   3.206%   $257.499   $257.50   $257.50   $257.50  
  Purchase #5 $54.61   13.390%   $61.9223   $61.92   $61.90   $61.90  
  Purchase #6 $59.92   9.321%   $65.5051   $65.51   $65.50   $65.50  
  Purchase #7 $200.70   3.351%   $207.4255   $207.43   $207.45   $207.40  
  7 purchase totals = $1,087.65       $1,178.6140   $1,178.62   $1,178.60   $1,178.50