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 $58.72   8.472%   $63.6948   $63.69   $63.70   $63.70  
  Purchase #2 $126.93   10.181%   $139.8527   $139.85   $139.85   $139.90  
  Purchase #3 $47.29   11.730%   $52.8371   $52.84   $52.85   $52.80  
  Purchase #4 $34.37   8.768%   $37.3836   $37.38   $37.40   $37.40  
  Purchase #5 $217.69   4.616%   $227.7386   $227.74   $227.75   $227.70  
  Purchase #6 $186.26   6.467%   $198.3054   $198.31   $198.30   $198.30  
  Purchase #7 $93.31   3.161%   $96.2595   $96.26   $96.25   $96.30  
  7 purchase totals = $764.57       $816.0717   $816.07   $816.10   $816.10