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 $112.55   10.852%   $124.7639   $124.76   $124.75   $124.80  
  Purchase #2 $108.98   3.845%   $113.1703   $113.17   $113.15   $113.20  
  Purchase #3 $104.55   10.560%   $115.5905   $115.59   $115.60   $115.60  
  Purchase #4 $166.50   11.752%   $186.0671   $186.07   $186.05   $186.10  
  Purchase #5 $158.66   5.533%   $167.4387   $167.44   $167.45   $167.40  
  Purchase #6 $206.42   5.677%   $218.1385   $218.14   $218.15   $218.10  
  Purchase #7 $134.93   5.284%   $142.0597   $142.06   $142.05   $142.10  
  7 purchase totals = $992.59       $1,067.2287   $1,067.23   $1,067.20   $1,067.30