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 $246.69   12.241%   $276.8873   $276.89   $276.90   $276.90  
  Purchase #2 $114.45   9.528%   $125.3548   $125.35   $125.35   $125.40  
  Purchase #3 $222.79   5.426%   $234.8786   $234.88   $234.90   $234.90  
  Purchase #4 $217.70   12.812%   $245.5917   $245.59   $245.60   $245.60  
  Purchase #5 $7.35   12.522%   $8.2704   $8.27   $8.25   $8.30  
  Purchase #6 $32.41   7.842%   $34.9516   $34.95   $34.95   $35.00  
  Purchase #7 $43.85   9.357%   $47.953   $47.95   $47.95   $48.00  
  7 purchase totals = $885.24       $973.8874   $973.88   $973.90   $974.10