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 $214.98   11.660%   $240.0467   $240.05   $240.05   $240.00  
  Purchase #2 $205.39   13.808%   $233.7503   $233.75   $233.75   $233.80  
  Purchase #3 $25.49   10.796%   $28.2419   $28.24   $28.25   $28.20  
  Purchase #4 $82.67   7.185%   $88.6098   $88.61   $88.60   $88.60  
  Purchase #5 $213.94   10.670%   $236.7674   $236.77   $236.75   $236.80  
  Purchase #6 $85.37   8.727%   $92.8202   $92.82   $92.80   $92.80  
  Purchase #7 $224.95   12.804%   $253.7526   $253.75   $253.75   $253.80  
  7 purchase totals = $1,052.79       $1,173.9889   $1,173.99   $1,173.95   $1,174.00