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 $55.26   9.759%   $60.6528   $60.65   $60.65   $60.70  
  Purchase #2 $235.60   7.558%   $253.4066   $253.41   $253.40   $253.40  
  Purchase #3 $127.36   12.737%   $143.5818   $143.58   $143.60   $143.60  
  Purchase #4 $79.41   3.755%   $82.3918   $82.39   $82.40   $82.40  
  Purchase #5 $87.74   12.334%   $98.5619   $98.56   $98.55   $98.60  
  Purchase #6 $36.49   13.742%   $41.5045   $41.50   $41.50   $41.50  
  Purchase #7 $225.48   6.238%   $239.5454   $239.55   $239.55   $239.50  
  7 purchase totals = $847.34       $919.6448   $919.64   $919.65   $919.70