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 $30.94   11.773%   $34.5826   $34.58   $34.60   $34.60  
  Purchase #2 $52.88   7.577%   $56.8867   $56.89   $56.90   $56.90  
  Purchase #3 $77.76   10.506%   $85.9295   $85.93   $85.95   $85.90  
  Purchase #4 $225.31   4.597%   $235.6675   $235.67   $235.65   $235.70  
  Purchase #5 $44.67   8.357%   $48.4031   $48.40   $48.40   $48.40  
  Purchase #6 $124.59   9.370%   $136.2641   $136.26   $136.25   $136.30  
  Purchase #7 $151.28   13.388%   $171.5334   $171.53   $171.55   $171.50  
  7 purchase totals = $707.43       $769.2669   $769.26   $769.30   $769.30