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 $236.67   12.704%   $266.7366   $266.74   $266.75   $266.70  
  Purchase #2 $133.83   4.800%   $140.2538   $140.25   $140.25   $140.30  
  Purchase #3 $178.57   3.611%   $185.0182   $185.02   $185.00   $185.00  
  Purchase #4 $64.94   13.392%   $73.6368   $73.64   $73.65   $73.60  
  Purchase #5 $53.93   5.600%   $56.9501   $56.95   $56.95   $57.00  
  Purchase #6 $126.85   6.375%   $134.9367   $134.94   $134.95   $134.90  
  Purchase #7 $198.75   4.600%   $207.8925   $207.89   $207.90   $207.90  
  7 purchase totals = $993.54       $1,065.4247   $1,065.43   $1,065.45   $1,065.40