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 $246.95   5.161%   $259.6951   $259.70   $259.70   $259.70  
  Purchase #2 $92.79   5.820%   $98.1904   $98.19   $98.20   $98.20  
  Purchase #3 $80.78   7.228%   $86.6188   $86.62   $86.60   $86.60  
  Purchase #4 $199.76   11.485%   $222.7024   $222.70   $222.70   $222.70  
  Purchase #5 $97.76   4.490%   $102.1494   $102.15   $102.15   $102.10  
  Purchase #6 $181.72   3.395%   $187.8894   $187.89   $187.90   $187.90  
  Purchase #7 $199.31   4.114%   $207.5096   $207.51   $207.50   $207.50  
  7 purchase totals = $1,099.07       $1,164.7551   $1,164.76   $1,164.75   $1,164.70