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 $32.53   6.292%   $34.5768   $34.58   $34.60   $34.60  
  Purchase #2 $188.96   7.416%   $202.9733   $202.97   $202.95   $203.00  
  Purchase #3 $212.98   3.168%   $219.7272   $219.73   $219.75   $219.70  
  Purchase #4 $217.27   4.823%   $227.7489   $227.75   $227.75   $227.70  
  Purchase #5 $202.68   13.381%   $229.8006   $229.80   $229.80   $229.80  
  Purchase #6 $108.61   8.489%   $117.8299   $117.83   $117.85   $117.80  
  Purchase #7 $30.64   13.844%   $34.8818   $34.88   $34.90   $34.90  
  7 purchase totals = $993.67       $1,067.5385   $1,067.54   $1,067.60   $1,067.50