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 $38.48   5.557%   $40.6183   $40.62   $40.60   $40.60  
  Purchase #2 $169.57   6.341%   $180.3224   $180.32   $180.30   $180.30  
  Purchase #3 $190.78   3.618%   $197.6824   $197.68   $197.70   $197.70  
  Purchase #4 $198.97   5.457%   $209.8278   $209.83   $209.85   $209.80  
  Purchase #5 $237.57   13.782%   $270.3119   $270.31   $270.30   $270.30  
  Purchase #6 $33.69   7.691%   $36.2811   $36.28   $36.30   $36.30  
  Purchase #7 $127.85   9.824%   $140.41   $140.41   $140.40   $140.40  
  7 purchase totals = $996.91       $1,075.4539   $1,075.45   $1,075.45   $1,075.40