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 $226.27   10.113%   $249.1527   $249.15   $249.15   $249.20  
  Purchase #2 $172.76   11.504%   $192.6343   $192.63   $192.65   $192.60  
  Purchase #3 $36.34   13.634%   $41.2946   $41.29   $41.30   $41.30  
  Purchase #4 $51.88   11.453%   $57.8218   $57.82   $57.80   $57.80  
  Purchase #5 $114.57   3.817%   $118.9431   $118.94   $118.95   $118.90  
  Purchase #6 $175.85   12.178%   $197.265   $197.27   $197.25   $197.30  
  Purchase #7 $227.60   6.461%   $242.3052   $242.31   $242.30   $242.30  
  7 purchase totals = $1,005.27       $1,099.4167   $1,099.41   $1,099.40   $1,099.40