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 $212.91   5.233%   $224.0516   $224.05   $224.05   $224.10  
  Purchase #2 $139.38   8.673%   $151.4684   $151.47   $151.45   $151.50  
  Purchase #3 $91.88   11.169%   $102.1421   $102.14   $102.15   $102.10  
  Purchase #4 $110.53   5.187%   $116.2632   $116.26   $116.25   $116.30  
  Purchase #5 $164.42   11.508%   $183.3415   $183.34   $183.35   $183.30  
  Purchase #6 $210.38   3.122%   $216.9481   $216.95   $216.95   $216.90  
  Purchase #7 $27.27   10.465%   $30.1238   $30.12   $30.10   $30.10  
  7 purchase totals = $956.77       $1,024.3387   $1,024.33   $1,024.30   $1,024.30