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 $195.95   5.436%   $206.6018   $206.60   $206.60   $206.60  
  Purchase #2 $48.34   3.156%   $49.8656   $49.87   $49.85   $49.90  
  Purchase #3 $38.29   13.320%   $43.3902   $43.39   $43.40   $43.40  
  Purchase #4 $232.55   7.562%   $250.1354   $250.14   $250.15   $250.10  
  Purchase #5 $229.44   3.863%   $238.3033   $238.30   $238.30   $238.30  
  Purchase #6 $221.83   12.721%   $250.049   $250.05   $250.05   $250.00  
  Purchase #7 $6.30   10.659%   $6.9715   $6.97   $6.95   $7.00  
  7 purchase totals = $972.70       $1,045.3168   $1,045.32   $1,045.30   $1,045.30