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 $61.25   4.428%   $63.9622   $63.96   $63.95   $64.00  
  Purchase #2 $222.97   11.208%   $247.9605   $247.96   $247.95   $248.00  
  Purchase #3 $114.50   11.697%   $127.8931   $127.89   $127.90   $127.90  
  Purchase #4 $227.47   9.535%   $249.1593   $249.16   $249.15   $249.20  
  Purchase #5 $45.77   13.648%   $52.0167   $52.02   $52.00   $52.00  
  Purchase #6 $178.37   11.863%   $199.53   $199.53   $199.55   $199.50  
  Purchase #7 $35.74   4.214%   $37.2461   $37.25   $37.25   $37.20  
  7 purchase totals = $886.07       $977.7679   $977.77   $977.75   $977.80