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 $57.94   8.294%   $62.7455   $62.75   $62.75   $62.70  
  Purchase #2 $225.97   10.180%   $248.9737   $248.97   $248.95   $249.00  
  Purchase #3 $49.31   12.197%   $55.3243   $55.32   $55.30   $55.30  
  Purchase #4 $239.70   7.319%   $257.2436   $257.24   $257.25   $257.20  
  Purchase #5 $169.34   13.663%   $192.4769   $192.48   $192.50   $192.50  
  Purchase #6 $122.28   6.255%   $129.9286   $129.93   $129.95   $129.90  
  Purchase #7 $87.97   3.319%   $90.8897   $90.89   $90.90   $90.90  
  7 purchase totals = $952.51       $1,037.5823   $1,037.58   $1,037.60   $1,037.50