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 $61.93   11.415%   $68.9993   $69.00   $69.00   $69.00  
  Purchase #2 $77.74   4.788%   $81.4622   $81.46   $81.45   $81.50  
  Purchase #3 $233.95   11.122%   $259.9699   $259.97   $259.95   $260.00  
  Purchase #4 $195.71   8.453%   $212.2534   $212.25   $212.25   $212.30  
  Purchase #5 $114.87   4.556%   $120.1035   $120.10   $120.10   $120.10  
  Purchase #6 $11.68   10.337%   $12.8874   $12.89   $12.90   $12.90  
  Purchase #7 $55.71   13.440%   $63.1974   $63.20   $63.20   $63.20  
  7 purchase totals = $751.59       $818.8731   $818.87   $818.85   $819.00