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 $60.88   13.269%   $68.9582   $68.96   $68.95   $69.00  
  Purchase #2 $15.32   11.412%   $17.0683   $17.07   $17.05   $17.10  
  Purchase #3 $32.83   10.195%   $36.177   $36.18   $36.20   $36.20  
  Purchase #4 $207.64   12.340%   $233.2628   $233.26   $233.25   $233.30  
  Purchase #5 $245.77   4.361%   $256.488   $256.49   $256.50   $256.50  
  Purchase #6 $123.67   11.844%   $138.3175   $138.32   $138.30   $138.30  
  Purchase #7 $153.90   12.858%   $173.6885   $173.69   $173.70   $173.70  
  7 purchase totals = $840.01       $923.9603   $923.97   $923.95   $924.10