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 $223.29   8.399%   $242.0441   $242.04   $242.05   $242.00  
  Purchase #2 $244.50   13.850%   $278.3633   $278.36   $278.35   $278.40  
  Purchase #3 $103.91   11.652%   $116.0176   $116.02   $116.00   $116.00  
  Purchase #4 $140.97   5.169%   $148.2567   $148.26   $148.25   $148.30  
  Purchase #5 $127.98   7.271%   $137.2854   $137.29   $137.30   $137.30  
  Purchase #6 $14.91   3.159%   $15.381   $15.38   $15.40   $15.40  
  Purchase #7 $13.93   9.725%   $15.2847   $15.28   $15.30   $15.30  
  7 purchase totals = $869.49       $952.6328   $952.63   $952.65   $952.70