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 $72.26   13.603%   $82.0895   $82.09   $82.10   $82.10  
  Purchase #2 $239.28   9.423%   $261.8274   $261.83   $261.85   $261.80  
  Purchase #3 $58.78   5.709%   $62.1358   $62.14   $62.15   $62.10  
  Purchase #4 $129.61   13.395%   $146.9713   $146.97   $146.95   $147.00  
  Purchase #5 $14.53   12.452%   $16.3393   $16.34   $16.35   $16.30  
  Purchase #6 $30.87   13.206%   $34.9467   $34.95   $34.95   $34.90  
  Purchase #7 $145.71   6.809%   $155.6314   $155.63   $155.65   $155.60  
  7 purchase totals = $691.04       $759.9414   $759.95   $760.00   $759.80