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 $177.44   13.623%   $201.6127   $201.61   $201.60   $201.60  
  Purchase #2 $52.73   6.375%   $56.0915   $56.09   $56.10   $56.10  
  Purchase #3 $105.60   8.734%   $114.8231   $114.82   $114.80   $114.80  
  Purchase #4 $75.94   10.122%   $83.6266   $83.63   $83.65   $83.60  
  Purchase #5 $172.71   3.800%   $179.273   $179.27   $179.25   $179.30  
  Purchase #6 $248.59   8.203%   $268.9818   $268.98   $269.00   $269.00  
  Purchase #7 $217.86   12.682%   $245.489   $245.49   $245.50   $245.50  
  7 purchase totals = $1,050.87       $1,149.8977   $1,149.89   $1,149.90   $1,149.90