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 $238.59   9.600%   $261.4946   $261.49   $261.50   $261.50  
  Purchase #2 $204.25   10.130%   $224.9405   $224.94   $224.95   $224.90  
  Purchase #3 $169.64   10.577%   $187.5828   $187.58   $187.60   $187.60  
  Purchase #4 $231.39   6.582%   $246.6201   $246.62   $246.60   $246.60  
  Purchase #5 $65.95   10.608%   $72.946   $72.95   $72.95   $72.90  
  Purchase #6 $27.26   12.176%   $30.5792   $30.58   $30.60   $30.60  
  Purchase #7 $173.30   12.541%   $195.0336   $195.03   $195.05   $195.00  
  7 purchase totals = $1,110.38       $1,219.1968   $1,219.19   $1,219.25   $1,219.10