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 $242.33   12.747%   $273.2198   $273.22   $273.20   $273.20  
  Purchase #2 $175.41   6.813%   $187.3607   $187.36   $187.35   $187.40  
  Purchase #3 $190.56   7.537%   $204.9225   $204.92   $204.90   $204.90  
  Purchase #4 $63.53   12.689%   $71.5913   $71.59   $71.60   $71.60  
  Purchase #5 $214.46   5.395%   $226.0301   $226.03   $226.05   $226.00  
  Purchase #6 $187.31   4.643%   $196.0068   $196.01   $196.00   $196.00  
  Purchase #7 $9.83   3.347%   $10.159   $10.16   $10.15   $10.20  
  7 purchase totals = $1,083.43       $1,169.2902   $1,169.29   $1,169.25   $1,169.30