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 $43.45   6.122%   $46.11   $46.11   $46.10   $46.10  
  Purchase #2 $226.57   10.161%   $249.5918   $249.59   $249.60   $249.60  
  Purchase #3 $127.36   11.569%   $142.0943   $142.09   $142.10   $142.10  
  Purchase #4 $120.61   7.860%   $130.0899   $130.09   $130.10   $130.10  
  Purchase #5 $21.64   8.592%   $23.4993   $23.50   $23.50   $23.50  
  Purchase #6 $74.39   6.248%   $79.0379   $79.04   $79.05   $79.00  
  Purchase #7 $187.72   7.338%   $201.4949   $201.49   $201.50   $201.50  
  7 purchase totals = $801.74       $871.9181   $871.91   $871.95   $871.90