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 $60.62   3.725%   $62.8781   $62.88   $62.90   $62.90  
  Purchase #2 $27.35   3.617%   $28.3392   $28.34   $28.35   $28.30  
  Purchase #3 $63.27   6.403%   $67.3212   $67.32   $67.30   $67.30  
  Purchase #4 $208.49   7.655%   $224.4499   $224.45   $224.45   $224.40  
  Purchase #5 $250.89   7.420%   $269.506   $269.51   $269.50   $269.50  
  Purchase #6 $11.81   5.311%   $12.4372   $12.44   $12.45   $12.40  
  Purchase #7 $134.92   4.237%   $140.6366   $140.64   $140.65   $140.60  
  7 purchase totals = $757.35       $805.5682   $805.58   $805.60   $805.40