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 $85.53   13.677%   $97.2279   $97.23   $97.25   $97.20  
  Purchase #2 $117.61   11.636%   $131.2951   $131.30   $131.30   $131.30  
  Purchase #3 $10.90   11.859%   $12.1926   $12.19   $12.20   $12.20  
  Purchase #4 $122.74   9.430%   $134.3144   $134.31   $134.30   $134.30  
  Purchase #5 $146.58   9.787%   $160.9258   $160.93   $160.95   $160.90  
  Purchase #6 $176.96   12.225%   $198.5934   $198.59   $198.60   $198.60  
  Purchase #7 $76.33   7.354%   $81.9433   $81.94   $81.95   $81.90  
  7 purchase totals = $736.65       $816.4925   $816.49   $816.55   $816.40