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 $46.81   11.670%   $52.2727   $52.27   $52.25   $52.30  
  Purchase #2 $242.80   11.149%   $269.8698   $269.87   $269.85   $269.90  
  Purchase #3 $219.41   4.719%   $229.764   $229.76   $229.75   $229.80  
  Purchase #4 $52.59   8.585%   $57.1049   $57.10   $57.10   $57.10  
  Purchase #5 $67.76   9.379%   $74.1152   $74.12   $74.10   $74.10  
  Purchase #6 $107.27   6.471%   $114.2114   $114.21   $114.20   $114.20  
  Purchase #7 $108.55   3.532%   $112.384   $112.38   $112.40   $112.40  
  7 purchase totals = $845.19       $909.7220   $909.71   $909.65   $909.80