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 $198.95   9.677%   $218.2024   $218.20   $218.20   $218.20  
  Purchase #2 $10.80   13.180%   $12.2234   $12.22   $12.20   $12.20  
  Purchase #3 $50.89   9.265%   $55.605   $55.61   $55.60   $55.60  
  Purchase #4 $215.68   5.768%   $228.1204   $228.12   $228.10   $228.10  
  Purchase #5 $43.53   4.353%   $45.4249   $45.42   $45.40   $45.40  
  Purchase #6 $125.74   6.549%   $133.9747   $133.97   $133.95   $134.00  
  Purchase #7 $236.44   12.858%   $266.8415   $266.84   $266.85   $266.80  
  7 purchase totals = $882.03       $960.3923   $960.38   $960.30   $960.30