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 $30.77   9.522%   $33.6999   $33.70   $33.70   $33.70  
  Purchase #2 $177.92   7.558%   $191.3672   $191.37   $191.35   $191.40  
  Purchase #3 $178.94   9.359%   $195.687   $195.69   $195.70   $195.70  
  Purchase #4 $23.69   3.855%   $24.6032   $24.60   $24.60   $24.60  
  Purchase #5 $7.65   5.268%   $8.053   $8.05   $8.05   $8.10  
  Purchase #6 $231.75   7.413%   $248.9296   $248.93   $248.95   $248.90  
  Purchase #7 $48.53   10.574%   $53.6616   $53.66   $53.65   $53.70  
  7 purchase totals = $699.25       $756.0015   $756.00   $756.00   $756.10