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 $222.69   10.720%   $246.5624   $246.56   $246.55   $246.60  
  Purchase #2 $40.32   9.471%   $44.1387   $44.14   $44.15   $44.10  
  Purchase #3 $246.69   8.595%   $267.893   $267.89   $267.90   $267.90  
  Purchase #4 $234.35   12.388%   $263.3813   $263.38   $263.40   $263.40  
  Purchase #5 $119.41   5.274%   $125.7077   $125.71   $125.70   $125.70  
  Purchase #6 $219.66   6.472%   $233.8764   $233.88   $233.90   $233.90  
  Purchase #7 $30.34   7.226%   $32.5324   $32.53   $32.55   $32.50  
  7 purchase totals = $1,113.46       $1,214.0919   $1,214.09   $1,214.15   $1,214.10