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 $56.99   9.562%   $62.4394   $62.44   $62.45   $62.40  
  Purchase #2 $132.39   5.422%   $139.5682   $139.57   $139.55   $139.60  
  Purchase #3 $37.29   10.777%   $41.3087   $41.31   $41.30   $41.30  
  Purchase #4 $66.92   11.209%   $74.4211   $74.42   $74.40   $74.40  
  Purchase #5 $46.26   10.742%   $51.2292   $51.23   $51.25   $51.20  
  Purchase #6 $250.99   10.520%   $277.3941   $277.39   $277.40   $277.40  
  Purchase #7 $113.97   12.671%   $128.4111   $128.41   $128.40   $128.40  
  7 purchase totals = $704.81       $774.7718   $774.77   $774.75   $774.70