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 $205.66   4.797%   $215.5255   $215.53   $215.55   $215.50  
  Purchase #2 $160.30   5.773%   $169.5541   $169.55   $169.55   $169.60  
  Purchase #3 $106.34   12.437%   $119.5655   $119.57   $119.55   $119.60  
  Purchase #4 $5.54   8.527%   $6.0124   $6.01   $6.00   $6.00  
  Purchase #5 $245.83   6.465%   $261.7229   $261.72   $261.70   $261.70  
  Purchase #6 $196.87   10.667%   $217.8701   $217.87   $217.85   $217.90  
  Purchase #7 $34.52   10.125%   $38.0152   $38.02   $38.00   $38.00  
  7 purchase totals = $955.06       $1,028.2657   $1,028.27   $1,028.20   $1,028.30