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 $48.32   13.326%   $54.7591   $54.76   $54.75   $54.80  
  Purchase #2 $161.78   6.223%   $171.8476   $171.85   $171.85   $171.80  
  Purchase #3 $136.71   4.422%   $142.7553   $142.76   $142.75   $142.80  
  Purchase #4 $177.88   13.223%   $201.4011   $201.40   $201.40   $201.40  
  Purchase #5 $48.33   5.578%   $51.0258   $51.03   $51.05   $51.00  
  Purchase #6 $37.61   13.546%   $42.7047   $42.70   $42.70   $42.70  
  Purchase #7 $208.46   4.575%   $217.997   $218.00   $218.00   $218.00  
  7 purchase totals = $819.09       $882.4906   $882.50   $882.50   $882.50