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 $50.27   12.539%   $56.5734   $56.57   $56.55   $56.60  
  Purchase #2 $169.37   9.157%   $184.8792   $184.88   $184.90   $184.90  
  Purchase #3 $187.81   10.411%   $207.3629   $207.36   $207.35   $207.40  
  Purchase #4 $187.92   4.587%   $196.5399   $196.54   $196.55   $196.50  
  Purchase #5 $141.54   11.156%   $157.3302   $157.33   $157.35   $157.30  
  Purchase #6 $62.36   8.563%   $67.6999   $67.70   $67.70   $67.70  
  Purchase #7 $176.57   6.558%   $188.1495   $188.15   $188.15   $188.10  
  7 purchase totals = $975.84       $1,058.5350   $1,058.53   $1,058.55   $1,058.50