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 $58.76   8.159%   $63.5542   $63.55   $63.55   $63.60  
  Purchase #2 $245.74   8.690%   $267.0948   $267.09   $267.10   $267.10  
  Purchase #3 $188.29   10.316%   $207.714   $207.71   $207.70   $207.70  
  Purchase #4 $93.29   5.837%   $98.7353   $98.74   $98.75   $98.70  
  Purchase #5 $29.30   3.225%   $30.2449   $30.24   $30.25   $30.20  
  Purchase #6 $91.61   11.259%   $101.9244   $101.92   $101.90   $101.90  
  Purchase #7 $191.88   5.208%   $201.8731   $201.87   $201.85   $201.90  
  7 purchase totals = $898.87       $971.1407   $971.12   $971.10   $971.10