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 $69.38   9.526%   $75.9891   $75.99   $76.00   $76.00  
  Purchase #2 $122.30   5.827%   $129.4264   $129.43   $129.45   $129.40  
  Purchase #3 $231.84   12.559%   $260.9568   $260.96   $260.95   $261.00  
  Purchase #4 $19.93   7.511%   $21.4269   $21.43   $21.45   $21.40  
  Purchase #5 $139.36   12.845%   $157.2608   $157.26   $157.25   $157.30  
  Purchase #6 $41.67   6.789%   $44.499   $44.50   $44.50   $44.50  
  Purchase #7 $169.91   4.820%   $178.0997   $178.10   $178.10   $178.10  
  7 purchase totals = $794.39       $867.6587   $867.67   $867.70   $867.70