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 $55.39   9.568%   $60.6897   $60.69   $60.70   $60.70  
  Purchase #2 $208.87   12.536%   $235.0539   $235.05   $235.05   $235.10  
  Purchase #3 $113.95   11.384%   $126.9221   $126.92   $126.90   $126.90  
  Purchase #4 $44.93   9.647%   $49.2644   $49.26   $49.25   $49.30  
  Purchase #5 $249.71   3.399%   $258.1976   $258.20   $258.20   $258.20  
  Purchase #6 $139.46   12.412%   $156.7698   $156.77   $156.75   $156.80  
  Purchase #7 $101.90   3.245%   $105.2067   $105.21   $105.20   $105.20  
  7 purchase totals = $914.21       $992.1042   $992.10   $992.05   $992.20