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 $119.53   5.797%   $126.4592   $126.46   $126.45   $126.50  
  Purchase #2 $128.45   13.659%   $145.995   $146.00   $146.00   $146.00  
  Purchase #3 $66.67   5.395%   $70.2668   $70.27   $70.25   $70.30  
  Purchase #4 $226.99   13.455%   $257.5315   $257.53   $257.55   $257.50  
  Purchase #5 $114.62   11.491%   $127.791   $127.79   $127.80   $127.80  
  Purchase #6 $186.29   13.636%   $211.6925   $211.69   $211.70   $211.70  
  Purchase #7 $33.80   3.230%   $34.8917   $34.89   $34.90   $34.90  
  7 purchase totals = $876.35       $974.6277   $974.63   $974.65   $974.70