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 $241.57   11.623%   $269.6477   $269.65   $269.65   $269.60  
  Purchase #2 $9.29   12.555%   $10.4564   $10.46   $10.45   $10.50  
  Purchase #3 $154.49   8.588%   $167.7576   $167.76   $167.75   $167.80  
  Purchase #4 $23.63   9.665%   $25.9138   $25.91   $25.90   $25.90  
  Purchase #5 $115.75   5.516%   $122.1348   $122.13   $122.15   $122.10  
  Purchase #6 $41.69   10.738%   $46.1667   $46.17   $46.15   $46.20  
  Purchase #7 $217.98   11.104%   $242.1845   $242.18   $242.20   $242.20  
  7 purchase totals = $804.40       $884.2615   $884.26   $884.25   $884.30