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 $27.71   7.177%   $29.6987   $29.70   $29.70   $29.70  
  Purchase #2 $202.99   5.247%   $213.6409   $213.64   $213.65   $213.60  
  Purchase #3 $18.73   10.484%   $20.6937   $20.69   $20.70   $20.70  
  Purchase #4 $233.69   12.196%   $262.1908   $262.19   $262.20   $262.20  
  Purchase #5 $201.26   11.528%   $224.4613   $224.46   $224.45   $224.50  
  Purchase #6 $67.96   13.430%   $77.087   $77.09   $77.10   $77.10  
  Purchase #7 $164.27   13.787%   $186.9179   $186.92   $186.90   $186.90  
  7 purchase totals = $916.61       $1,014.6903   $1,014.69   $1,014.70   $1,014.70