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 $57.69   7.753%   $62.1627   $62.16   $62.15   $62.20  
  Purchase #2 $110.62   11.855%   $123.734   $123.73   $123.75   $123.70  
  Purchase #3 $113.61   3.696%   $117.809   $117.81   $117.80   $117.80  
  Purchase #4 $37.88   4.842%   $39.7141   $39.71   $39.70   $39.70  
  Purchase #5 $164.69   7.860%   $177.6346   $177.63   $177.65   $177.60  
  Purchase #6 $122.81   11.478%   $136.9061   $136.91   $136.90   $136.90  
  Purchase #7 $248.25   11.466%   $276.7143   $276.71   $276.70   $276.70  
  7 purchase totals = $855.55       $934.6748   $934.66   $934.65   $934.60