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 $213.90   11.864%   $239.2771   $239.28   $239.30   $239.30  
  Purchase #2 $121.77   3.364%   $125.8663   $125.87   $125.85   $125.90  
  Purchase #3 $50.87   11.255%   $56.5954   $56.60   $56.60   $56.60  
  Purchase #4 $91.96   6.462%   $97.9025   $97.90   $97.90   $97.90  
  Purchase #5 $70.34   8.259%   $76.1494   $76.15   $76.15   $76.10  
  Purchase #6 $218.90   9.283%   $239.2205   $239.22   $239.20   $239.20  
  Purchase #7 $18.87   5.471%   $19.9024   $19.90   $19.90   $19.90  
  7 purchase totals = $786.61       $854.9136   $854.92   $854.90   $854.90