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 $208.65   11.490%   $232.6239   $232.62   $232.60   $232.60  
  Purchase #2 $229.91   13.722%   $261.4583   $261.46   $261.45   $261.50  
  Purchase #3 $162.50   8.741%   $176.7041   $176.70   $176.70   $176.70  
  Purchase #4 $187.75   7.310%   $201.4745   $201.47   $201.45   $201.50  
  Purchase #5 $30.61   7.324%   $32.8519   $32.85   $32.85   $32.90  
  Purchase #6 $235.57   12.617%   $265.2919   $265.29   $265.30   $265.30  
  Purchase #7 $131.92   3.628%   $136.7061   $136.71   $136.70   $136.70  
  7 purchase totals = $1,186.91       $1,307.1107   $1,307.10   $1,307.05   $1,307.20