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 $44.44   5.464%   $46.8682   $46.87   $46.85   $46.90  
  Purchase #2 $20.81   6.397%   $22.1412   $22.14   $22.15   $22.10  
  Purchase #3 $15.25   6.632%   $16.2614   $16.26   $16.25   $16.30  
  Purchase #4 $41.58   7.112%   $44.5372   $44.54   $44.55   $44.50  
  Purchase #5 $199.35   11.785%   $222.8434   $222.84   $222.85   $222.80  
  Purchase #6 $88.69   4.640%   $92.8052   $92.81   $92.80   $92.80  
  Purchase #7 $17.79   5.161%   $18.7081   $18.71   $18.70   $18.70  
  7 purchase totals = $427.91       $464.1647   $464.17   $464.15   $464.10