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 $184.49   9.769%   $202.5128   $202.51   $202.50   $202.50  
  Purchase #2 $73.96   6.789%   $78.9811   $78.98   $79.00   $79.00  
  Purchase #3 $165.26   4.532%   $172.7496   $172.75   $172.75   $172.70  
  Purchase #4 $124.43   7.260%   $133.4636   $133.46   $133.45   $133.50  
  Purchase #5 $104.49   9.341%   $114.2504   $114.25   $114.25   $114.30  
  Purchase #6 $183.54   4.782%   $192.3169   $192.32   $192.30   $192.30  
  Purchase #7 $225.96   6.542%   $240.7423   $240.74   $240.75   $240.70  
  7 purchase totals = $1,062.13       $1,135.0167   $1,135.01   $1,135.00   $1,135.00