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 $229.62   4.212%   $239.2916   $239.29   $239.30   $239.30  
  Purchase #2 $174.98   11.211%   $194.597   $194.60   $194.60   $194.60  
  Purchase #3 $241.35   8.541%   $261.9637   $261.96   $261.95   $262.00  
  Purchase #4 $75.73   5.484%   $79.883   $79.88   $79.90   $79.90  
  Purchase #5 $191.56   3.682%   $198.6132   $198.61   $198.60   $198.60  
  Purchase #6 $146.85   11.176%   $163.262   $163.26   $163.25   $163.30  
  Purchase #7 $62.33   11.793%   $69.6806   $69.68   $69.70   $69.70  
  7 purchase totals = $1,122.42       $1,207.2911   $1,207.28   $1,207.30   $1,207.40