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 $235.35   8.591%   $255.5689   $255.57   $255.55   $255.60  
  Purchase #2 $136.36   13.106%   $154.2313   $154.23   $154.25   $154.20  
  Purchase #3 $31.66   8.605%   $34.3843   $34.38   $34.40   $34.40  
  Purchase #4 $194.82   13.321%   $220.772   $220.77   $220.75   $220.80  
  Purchase #5 $209.48   11.445%   $233.455   $233.46   $233.45   $233.50  
  Purchase #6 $200.57   12.862%   $226.3673   $226.37   $226.35   $226.40  
  Purchase #7 $79.69   5.312%   $83.9231   $83.92   $83.90   $83.90  
  7 purchase totals = $1,087.93       $1,208.7019   $1,208.70   $1,208.65   $1,208.80