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 $249.83   6.426%   $265.8841   $265.88   $265.90   $265.90  
  Purchase #2 $155.38   4.678%   $162.6487   $162.65   $162.65   $162.60  
  Purchase #3 $148.45   6.414%   $157.9716   $157.97   $157.95   $158.00  
  Purchase #4 $130.55   4.558%   $136.5005   $136.50   $136.50   $136.50  
  Purchase #5 $123.37   12.684%   $139.0183   $139.02   $139.00   $139.00  
  Purchase #6 $250.62   9.164%   $273.5868   $273.59   $273.60   $273.60  
  Purchase #7 $211.59   3.296%   $218.564   $218.56   $218.55   $218.60  
  7 purchase totals = $1,269.79       $1,354.1740   $1,354.17   $1,354.15   $1,354.20