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 $67.64   11.603%   $75.4883   $75.49   $75.50   $75.50  
  Purchase #2 $234.83   6.335%   $249.7065   $249.71   $249.70   $249.70  
  Purchase #3 $85.95   11.381%   $95.732   $95.73   $95.75   $95.70  
  Purchase #4 $24.57   4.660%   $25.715   $25.72   $25.70   $25.70  
  Purchase #5 $139.60   10.383%   $154.0947   $154.09   $154.10   $154.10  
  Purchase #6 $163.91   9.325%   $179.1946   $179.19   $179.20   $179.20  
  Purchase #7 $160.55   12.133%   $180.0295   $180.03   $180.05   $180.00  
  7 purchase totals = $877.05       $959.9606   $959.96   $960.00   $959.90