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 $48.44   13.567%   $55.0119   $55.01   $55.00   $55.00  
  Purchase #2 $156.93   10.200%   $172.9369   $172.94   $172.95   $172.90  
  Purchase #3 $164.36   11.667%   $183.5359   $183.54   $183.55   $183.50  
  Purchase #4 $42.30   9.237%   $46.2073   $46.21   $46.20   $46.20  
  Purchase #5 $94.95   3.332%   $98.1137   $98.11   $98.10   $98.10  
  Purchase #6 $100.26   13.811%   $114.1069   $114.11   $114.10   $114.10  
  Purchase #7 $240.72   8.117%   $260.2592   $260.26   $260.25   $260.30  
  7 purchase totals = $847.96       $930.1718   $930.18   $930.15   $930.10