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 $250.48   7.630%   $269.5916   $269.59   $269.60   $269.60  
  Purchase #2 $44.65   12.231%   $50.1111   $50.11   $50.10   $50.10  
  Purchase #3 $230.54   12.698%   $259.814   $259.81   $259.80   $259.80  
  Purchase #4 $52.76   9.441%   $57.7411   $57.74   $57.75   $57.70  
  Purchase #5 $187.41   8.256%   $202.8826   $202.88   $202.90   $202.90  
  Purchase #6 $169.26   11.431%   $188.6081   $188.61   $188.60   $188.60  
  Purchase #7 $249.77   9.360%   $273.1485   $273.15   $273.15   $273.10  
  7 purchase totals = $1,184.87       $1,301.8970   $1,301.89   $1,301.90   $1,301.80