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 $228.74   12.105%   $256.429   $256.43   $256.45   $256.40  
  Purchase #2 $158.25   12.157%   $177.4885   $177.49   $177.50   $177.50  
  Purchase #3 $28.43   12.543%   $31.996   $32.00   $32.00   $32.00  
  Purchase #4 $90.36   13.728%   $102.7646   $102.76   $102.75   $102.80  
  Purchase #5 $110.62   8.304%   $119.8059   $119.81   $119.80   $119.80  
  Purchase #6 $195.58   11.256%   $217.5945   $217.59   $217.60   $217.60  
  Purchase #7 $153.49   6.162%   $162.9481   $162.95   $162.95   $162.90  
  7 purchase totals = $965.47       $1,069.0266   $1,069.03   $1,069.05   $1,069.00