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 $116.94   7.290%   $125.4649   $125.46   $125.45   $125.50  
  Purchase #2 $54.51   11.381%   $60.7138   $60.71   $60.70   $60.70  
  Purchase #3 $40.86   8.335%   $44.2657   $44.27   $44.25   $44.30  
  Purchase #4 $207.77   12.757%   $234.2752   $234.28   $234.30   $234.30  
  Purchase #5 $186.71   8.390%   $202.375   $202.38   $202.40   $202.40  
  Purchase #6 $183.32   4.342%   $191.2798   $191.28   $191.30   $191.30  
  Purchase #7 $206.96   11.566%   $230.897   $230.90   $230.90   $230.90  
  7 purchase totals = $997.07       $1,089.2714   $1,089.28   $1,089.30   $1,089.40