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 $58.79   8.210%   $63.6167   $63.62   $63.60   $63.60  
  Purchase #2 $164.41   6.154%   $174.5278   $174.53   $174.55   $174.50  
  Purchase #3 $148.86   7.665%   $160.2701   $160.27   $160.25   $160.30  
  Purchase #4 $129.95   3.677%   $134.7283   $134.73   $134.75   $134.70  
  Purchase #5 $217.92   8.119%   $235.6129   $235.61   $235.60   $235.60  
  Purchase #6 $32.40   7.607%   $34.8647   $34.86   $34.85   $34.90  
  Purchase #7 $87.68   10.214%   $96.6356   $96.64   $96.65   $96.60  
  7 purchase totals = $840.01       $900.2561   $900.26   $900.25   $900.20